maybe he's talking about a 64 4000+ or maybe a 64 x2 4000+ and thought 4000+ number referred to its clock speed.
and stay far far away from the 5200. it is slow. you'll be lucky to get playable frame rates at 800x600, depending on the game and the settings. if you want an old agp card, find a ti4600, a ti4800, or a radeon 9600, 9700, or 9800. all of those cards are better than the 5200. in fact. stay away from the whole nividea 5xxx line. the 5900s were decent (for their time), but pretty much the rest of the lines sucks. and now that they are several years old, they just aren't worth it.
go for a x800, a 9800, a 6800, a 6600, or at the low end, a 9600xt if you want a cheap agp card.
and, if you are building a new system, you really should go PCI-e. agp is very much a dying technology.