Yeah it really is time to get a new PC and they are a lot cheaper than they used to be. You won't find up to date drivers for the old hardware now and it will just get worse. Anyway you're going to love the difference in speed and reliability.
When you get your new one set up you can copy over anything you want to keep.
I'm the wrong person to advise where to get one though because I always buy the parts and build my own. There was a long thread on MN just recently where someone wanted a new reasonably priced PC. Maybe you can find it, but if not then start one with something like that in the title and there will be lots of suggestions.
Most will come with Windows Vista now, but you might get a bargain if you have one with XP on. Personally I'm putting off having Vista until they get the bugs out of it. XP is just so stable.
Don't worry too much about the speed of the new one. They will all be 5-6 times faster than you have so it's not worth paying extra just to get one that's 7 times faster.
Look for 1GB ram if having XP but preferably 2GB ram if having Vista because it uses an awful lot just for the operating system to run.
Hard drives won't be smaller than 80GB anyway now which is enough for most people unless you expect to have an awful lot of music/photos. Sata hard drives are better, but again not worth paying a fortune for.
You will probably want a flat screen monitor. You can use your old one, but I expect that's getting on a bit and the flat ones are far better.
Graphics cards. Unless you play state of the art games any graphics card they come with will be fine. Many don't have one at all since it's handled on the motherboard.
USB ports. They mostly have them on the front as well as the back. This matters if you're going to be plugging cameras etc into it.
That's all I can think of for now, but others will have suggestions. Maybe the poster from the other week got one after all and can say how good it was.