Sorry for not replying earlier, I've been rather busy with deadlines and things recently.

There are a lot of things which could be causing this problem. You say it only happens about half the time you use your computer? That sounds a bit odd, usually it's all or nothing. It could be an ISP-related problem, as it only affects some sites. Another possibility is that you've picked up a nasty bit of spyware along the way. The fact that internet explorer crashes often suggests this, but the crashes could also be caused by a botched installation of something (a friend had a problem in that the adobe site would crash his computer due to some obscure javascript/flash-related bug. Never did solve that one). You could try uninstalling any software/patches that were installed just before the problem started to occur. Make sure you keep the definitions up to date in any antivirus or antispyware program you use (and you *should* be using a firewall as well as antivirus and antispyware). You could try disabling ActiveX and javascript, and see if that solves the problem.

Hmmm, come to think of it it may be hardware (the above problem seemed to involve the graphics card in some obscure way). Check any newly added hardware, try reseating it, try flashing the BIOS. Come to think of it, you could try checking the capacitors on the motherboard. There were a lot of dodgy ones at one point (thanks to some coporate espionage that went wrong). If any of the caps are bulging or leaking stuff, then the motherboard's screwed.