Tech Guy came and spent several hours going over my computer today without finding any one thing that was causing the problem - but so far, at least, it seems to be crashing far less so long as I don't use Search and Destroy to scan things and switch to Yahoo for my spyware needs. It has now been on for several hours downloading stuff and looking at sites.
His thinking is that I may need to upgrade my AGP video card which is only 64 meg and is having to cope with what, when it works, is a moderately fast system. Any volunteers to help me install this at some point, because he is not coming back? At some point I need to put more RAM in anyway.