Older Macbook Pro Locking Up Every Few Minutes, Help Troubleshooting Please

Question

Hi Folks,
I've been having problems with the trackpad click-bar acting up, but now suddenly the computer is repeatedly freezing/locking up.  Each time I have to use the power button to turn it off, then reboot.
How can I start figuring out what the heck is wrong with it?  I'm not even sure what log in console would be useful, if any??  Are there any free or cheap programs that will actually monitor the computer for this sort of problem and record and decipher what is causing the lockups/freezes?  Sometimes the screen goes black while the computer is clearly still running, and I cannot get it back without restarting.  More often, I'll be in the middle of selecting a menu item, or loading a new tab, or some activity like that, and the screen/computer just freezes, sometimes even with a ghostly image of the drop down menu selection that I'd just selected still showing - and the computer is totally unresponsive to anything, e.g., won't select anything, won't respond to trying to get the finder or system preferences up, just totally frozen.  Won't respond to cmd-opt-esc either.  Sometimes I'll get the spinning rainbow wheel, rather than no activity, but it will just spin forever, it's not managing to do anything. 
Info:
15" macbook pro, probably late 2006/early 2007 model, 2 GHz intel core duo, 2 GB memory, OS X 10.5.8 (e.g., it's NOT under warranty, I'm on my own, and $$s are VERY tight, I need to do everything I can to figure this out myself)
Typically, all I'm doing is browsing the web - so usually all I have open is a magicjack (internet phone), and a web browser.  Usually I use firefox (most current version) - but it's locking up even with firefox off and using safari (5.0.4).  It does seem to crash faster with firefox, but still far too often with Safari (like every 30 min perhaps instead of 10, this is bad!).  In other words, I'm not putting it under heavy load.
It's running off of AC power, not battery (although I gather that a bad battery can still cause problems when running off AC, is that even correct?).  I have external speakers plugged into it because often if watching streaming video the volume is too low if just using the computer's speakers.  Using cox high speed internet off ethernet. 
I've tried letting the computer stay off for 10 min or so then rebooting, it still freezes.
I installed the sophos (sp?) anti-virus, checked the computer, no virus's/trojans/worms.
I don't know where to go from here, please help!

Answer 1

CMCSK, if I have installation disks, I can't find them quickly.  I've emailed the friend who gave me this computer asking if they recall sending any or not.
In the meantime, I just ran disk utility verify disk permissions and got this:
Verify permissions for “Macintosh HD”
          Reading permissions database.
          Reading the permissions database can take several minutes.
Permissions differ on "private/var/log/secure.log", should be -rw------- , they are -rw-r----- .
Permissions differ on "System/Library/CoreServices/Front Row.app/Contents/CodeResources", should be -rw-r--r-- , they are lrwxr-xr-x .
Permissions differ on "System/Library/CoreServices/Front Row.app/Contents/PlugIns/DVD.frappliance/Contents/CodeResources", should be -rw-r--r-- , they are lrwxr-xr-x .
Permissions differ on "System/Library/CoreServices/Front Row.app/Contents/PlugIns/FRSettings.frappliance/Contents/CodeResources", should be -rw-r--r-- , they are lrwxr-xr-x .
Permissions differ on "System/Library/CoreServices/Front Row.app/Contents/PlugIns/FRSources.frappliance/Contents/CodeResources", should be -rw-r--r-- , they are lrwxr-xr-x .
Permissions differ on "System/Library/CoreServices/Front Row.app/Contents/PlugIns/Movies.frappliance/Contents/CodeResources", should be -rw-r--r-- , they are lrwxr-xr-x .
Permissions differ on "System/Library/CoreServices/Front Row.app/Contents/PlugIns/Music.frappliance/Contents/CodeResources", should be -rw-r--r-- , they are lrwxr-xr-x .
Permissions differ on "System/Library/CoreServices/Front Row.app/Contents/PlugIns/Photos.frappliance/Contents/CodeResources", should be -rw-r--r-- , they are lrwxr-xr-x .
Permissions differ on "System/Library/CoreServices/Front Row.app/Contents/PlugIns/Podcasts.frappliance/Contents/CodeResources", should be -rw-r--r-- , they are lrwxr-xr-x .
Permissions differ on "System/Library/CoreServices/Front Row.app/Contents/PlugIns/TV.frappliance/Contents/CodeResources", should be -rw-r--r-- , they are lrwxr-xr-x .
Permissions differ on "System/Library/PrivateFrameworks/BackRow.framework/Versions/A/CodeResources", should be -rw-r--r-- , they are lrwxr-xr-x .
Group differs on "Library/PreferencePanes", should be 0, group is 80.
Permissions differ on "Library/PreferencePanes", should be drwxr-xr-x , they are drwxrwxr-x .
Warning: SUID file "System/Library/Filesystems/AppleShare/afpLoad" has been modified and will not be repaired.
Warning: SUID file "System/Library/PrivateFrameworks/DiskManagement.framework/Versions/A/Resources /DiskManagementTool" has been modified and will not be repaired.
Warning: SUID file "bin/rcp" has been modified and will not be repaired.
Warning: SUID file "usr/bin/rlogin" has been modified and will not be repaired.
Warning: SUID file "usr/bin/rsh" has been modified and will not be repaired.
Warning: SUID file "usr/sbin/pppd" has been modified and will not be repaired.
Warning: SUID file "usr/sbin/vpnd" has been modified and will not be repaired.
ACL found but not expected on "private".
Permissions verification complete
I ran it still connected to internet, etc., So, in the meantime, until I can find or figure out if I've even got installation disks, I'll go ahead and disconnect everything, reboot normally, then use disk utility to run verify permissions again & assuming it still finds problem, use repair permissions.  I've no idea what the SUID warnings mean, or if anything needs to be done about them.