Macbook OS X 10.5.8 Lagging - Please help!

Question

Hi,
I've been having problems with my Macbook recently.. It keeps lagging for a good couple minutes. This is even without any programs/applications running (I do not have any Login Items). It even lags when I go to type in my password at login (there is only one user) after starting my computer. The lags are random, to the best of my knowledge, but relatively frequent and sometimes in rapid succession. It'll suddenly lag when I move my mouse, when I try bringing up my dashboard via keyboard shortcut, when I try opening Finder, etc. I also did not receive a Mac OS X Install Disc when I purchased my Macbook at the Apple store (if I was supposed to buy it, I guess I opted out - which I am beginning to regret). I'm not very tech savvy but if I could get any advice/help, I would greatly appreciate it. Ive included details of my macbook that I thought might be helpful/relevant below:
I think I might have bought it either 2007 or 2008?
Mac OS X 10.5.8
Processor:  2.4 GHz Intel Core 2 Duo
Memory:  2 GB 667 MHz DDR2 SDRAM
Macintosh HD:
  Capacity:    148.73 GB
  Available:    51.84 GB
S.M.A.R.T. status:    Verified
Hardware Overview:
  Model Name:    MacBook
  Model Identifier:    MacBook4,1
  L2 Cache:    3 MB
  Memory:    2 GB
Please let me know if you need any other information. Thank you!

Answer 1

P.s.  By "lagging" I mean that sometimes my entire screen freezes (and I may or may not be able to move the mouse, the mouse may or may not turn into the dreaded pinwheel), sometimes its just a program/app, sometimes finder/dock/corner-shortcuts will freeze and i'll be able to use a program/app (like firefox or textedit) while I wait for lag to pass.. but usually, a freezing in a program/app will be followed by the freezing of finder/dock/corner-shortcuts/bar-at-the-top, or vica versa, and everything will just freeze. (Ugh, my computer froze multiple times while trying to add this edit - with the longest lag/freeze lasting about 5 minutes, I believe - which is why I missed the 15 min time frame to edit my post.)