ok i've dealt with problems like this before.
Again try to get it to go into Safe Mode.
When you get to the screen to choose safe mode, it will display a LOT of files loading.
A lot of times with problems like these, it may get to a file then just freeze the system. Now, even during normal access to safe mode, it will freeze for several seconds but if it freezes on loading a certain file for a long time, like 5 minutes straight, then it may be inaccessible.
Windows Updates will also cause this problem as well. I've worked on many pcs who use the windows updates like crazy and eventually, one update will conflict and cause this same problem.
My advice-
For one, do not use Windows Updates. They are mostly just security fixes. Since he runs 3rd party security (you will actually need virus\spyware protection and firewall) he doesnt need windows updates.
Two, if u cant get into safe mode, the only thing left really is to find out if he needs anything backed up before u wipe out his hard drive!
If he doesnt know what to ask or where things are, these are typical places of interest to keep-
C:\Documents and Settings\(his user name)\My Documents
C:\Documents and Settings\(his user name)\Favorites
This will take care of most default saved locations and his bookmarks if he has been using Internet Explorer.
If he uses Firefox, go here-
C:\Documents and Settings\(his user name)\Application Data\Mozilla\Firefox\Profiles
there is a directory in there called something weird, go in there then get the bookmarks.html
That file keeps ALL firefox bookmarks so that's his favorites for Firefox if he uses that.
Also, check in C:\Program Files for installed software. This way you can write down everythign he has installed and see if he has the discs for them still. If he doesn't, then at least you have a list so he isn't missing something that he can't remember what it is.
To backup all this data, you will need to pull the drive out of his pc, where all the cables are wired, set the jumper to SLAVE and hook it up to your computer via the same cable as your Master drive. You will need to make sure you set your Master drive to MAster with slave present if it isnt already.
If you decide to hookup his drive via a separate cable that connects to it's own connector, you will need to set his drive to just MASTER or MASTER with no slave present.
If he has no jumpers, then it's SATA or SATAII and this info is irrelevant.
Go into windows and find all of these files from there.
When you are done, take his hard drive out, AFTER you shut the computer down. Never hookup the drive with pc on either. And, never touch the circuit board unless you are grounded.
Now, put his drive back in his pc, make sure his is set back as master if need be and pop in a Windows XP disc and it will allow him to format his drive then reinstall windows xp.
Do a quick format as it sounds like the hardware is still fine. IT will ask this.
Once everything is back in windows, u say his pc only has 256mb of RAM... thats not enough for fast preformance. PM me when you get his pc back up in windows and i'll have you forward me his services list so i can tell you how to Optimize his pc(very easy, just do as i say) and it will free up memory from 10-80MB depending on what all is turned on that he will never use.
This will allow him to have ALL security required to be protected and still have some memory left over before his pc starts slowing down again.