Hi Graham,
I've just upgraded recently and am running an Nforce 4 Gigabyte board (K8N51GMF-9).
It has the 6100 on which i used for a week while i was waiting for a PCI-E 7600GT Card.
Im currently running an Athlon64 3200+ and 2GB Ram. I also had a 5200FX in my old system.
Performance seemed slightly better on the 6100 than the 5200 however the 7600GT is rapid (ie, Metal Gear 2, FarCry etc all run at full detail @ 1280x1024) and run at reasonable speeds - no jitter etc.
The machines been stable, it has the 939Socket so can goto more or less any Athlon64/FX/DualCore chip on the market with ease.
I think the performance of the 6100 may have stayed good because i'm running 2GB of DDR533 on Dual Channel and i allocated a lump to the 6100.
In my eyes id get the better board and get a 7300LE card (or something similar) thats about 6-8 times quicker than an FX5200 and can be had for about £60.
Good luck
I wish someone would just call me Sir, without adding 'Your making a scene'.
Rob