You are not going to want to mess with your RAM, and who knows what CPU that motherboard can support. But one thing is for sure, you need to get a new video card. By far your weakest component is that GF2MX.
I would say $120 on a radeon 9800 pro would do you well. You could also spend $160 and get an AGP GF6600GT. Not sure if your power supply would handle the 6600GT or not.
In some games such as farcry and NFSU2 you will be CPU bottlenecked and not get the full performance out of the new cards. In others, the cards will make an even bigger difference. either way, compared to the GF2 MX, night and day difference in todays games.
Toms hardware just did a little $250 upgrade guide. Look on the homepage as they took an Athlon XP2000+ and upgraded the memory and video card, showing the improvements. Doom 3 had a huge boost. It would be a good read for you.
As far as lasting a couple years, that depends. I'd say it could probably meet minimum specs for almost any game coming out in the next two years, but resolution and detail levels will have to get dumbed way down to remain playable. Then again, (and no offense meant), if you have been happy with a GF2 MX up til now, you'll probably be happy with a 9800 pro GF6600GT for a couple more years. I'd say even though there is no guarantees for future titles, invest $120 in the 9800 pro and enjoy current games alot more. You need to dump the GF2MX.
Older game, <A HREF="http://www.ixbt.com/video2/over2k4-ut-1024.shtml" target="_new">but just look at</A> the GF2 MX compared to a 9800 pro in UT2003.
<A HREF="http://service.futuremark.com/compare?3dm05=658042" target="_new">3DMark05</A> <A HREF="http://service.futuremark.com/compare?2k3=3781954" target="_new">3DMark03</A>
<P ID="edit"><FONT SIZE=-1><EM>Edited by pauldh on 07/18/05 10:09 PM.</EM></FONT></P>