Very slow to boot, even on an external drive

Question

A friend's 15" MacBook Pro, quad core i7,(older, not sure of the exact model) very slow to boot, and boots with the progress bar, then when you try to log in, it goes back to the login page. Often it will not start. Starts after resetting SMC.  Reset PRAM. Booted to the recovery disk, ran repair disk on drive, no errors, tried to run repair on the volume and the MBP shut down. Tried booting to an external drive and it boots to an empty desktop with a finder window like an extended desktop.Tried AHT, only the usual battery sensor error, 4SNS/1/40000000  TB3T-128.000. ran extended test, same thing, only the one error.
So, how to back up this MB Pro before I try an erase and install. (short of removing the drive) It would seem to be a hardware error, but always want to try an erase and install. Any ideas or troubleshooting suggestions?

Answer 1

Mike -- thanks for your input. I guess Windows is just a worrisome thing for us Mac guys. Part of what always gets me is unknown code that goes into Windows. I did a Google the other day to see if I could get a feel for the "roots" of the upcoming Vista.
Who knows what Vista is really based on -- a modification of NT that was in part based on DOS and VMS? From my limited experience, I am not sure there is enough shelf space to hold the manuals to run VMS successfully. Of course, why worry; Boot Camp and other things will change before Vista gets here.
The bottom line is that I will use all the Windows security fixes.
Mac Mini (Intel Core Duo)   Mac OS X (10.4.5)