Even if you spent the money, it won't allow you to do anything more.
we're not just telling you this for fun, you simply will not get anything aproaching modern day quality. anything more than web browsing and a socket 939 is entirely useless.
the best you can get will be a 4800+ i believe (and even then, the motherboard might not support it). which is a 2.4ghz dual core. but just because its a 2.4 dual, its not going to give you 'good performance'. it would be orders of magnitude weaker than a i3 2100. and you probably won't find one at a reasonable price.
given the cost of a Pentium g620, a cheap h61 mobo and 2gb of ram, it would not cost you much to get a PC that actually performs well in modern applications.
I completely disagree with the posts about the socket 939 system. What i do agree with is that 939 systems are old. I currently use a 939 system and it runs everything perfectly, World of Warcraft: Mists of Pandora (latest verson of WoW) works great w/ 65 fps and 35 fps at peek pve/pvp combat.
2 GB Ram
9800GT w/ 512mb
2x 1 TB Spinpoint Sata 3 gb/s HDDs configured for Raid 0
Windows XP Pro
all w/ stock settings, no OC
I plan on getting another 2 GB of ram and installing Windows 7 while I think about the next system I will build, most likely an AM3+ and use the 9800GT video card I have untill i'm ready to upgrade.
A socket 939 system is more than enuff to play old games and even some new games. Just dont spend more than $100 on parts.
The best Socket 939 CPU is Opteron 185 or FX-60
You will not be able to have more than 2 GB of ram if you use a 32bit OS
Also think about using your 939 system for a HTPC running Ubuntu 12.04, when you finally build a new system.
I agree with LordEricX, Opti185 and max out your ram and a decent old graphics card will allow you to play plenty of older games and a few newer at low to medium resolution depending on the graphics card.