well i have Asrock mobo 939 and u can put am2 upgrade in, but i just got AMD 4400 x2 CPU socket 939 in and it runs fine, since to totally upgrade to am2 u need upgrade card, CPU and Mem, its cheaper to just get 939 cpu
there is little difference between cpu in ranges 4400 4800 u score better on benchmarks but wont see any difference for yourself
games usually bottle neck on your vid Card first then on cpu, memory is least bottle neck as it already fast, my DDR 400 mem is 5000mbs and DDR2 800 8000mbs tested
i would get any dual core CPU like 4000+ and then better video card if needed
The extra $15 is worth it even if there weren't compatibility issues with the upgrades... but there are issues with your $160 upgrade. AM2 uses DDR2 and S939 uses DDR. You can't interchange any mobo, CPU, memory combo between AM2 and 939 which has been really irritating for S939 owners since S939 prices are so much lower than AM2 now.
Overall though I'm not sure if an upgrade is really worthwhile at this point. See how games play first and then worry about upgrading. If things play well enough I wouldn't worry about bottlenecking at the moment. As always its best to wait as long as possible between upgrades to get the most added performance for your money.
For $160, I can get:
AMD 4400+ s939
1GB DDR400 RAM
If this is the case, then I would say, no. It's not worth it. I've been running just fine with my rig (see specs below). I've heard some unpleasant things about the AM2CPU board (like it sits loose) and I'm not sure just how upgradeable it is. Can you put an AM2 5200+ in there?
i recently upgraded from my skt939, 3200+ venice, 1 gig 400 dual channel to am2, 5600+, 2gig 800 dual channel and it has made an unexpectedly big difference for gaming even though i still have me ole 6600GT. on WoW i get about or not quite twice the fps @ 1024x768 with max candy settings. on Insurgency (a source mod) i get atleast 3 or 4 times the fps @ 1024x768 with max candy and 20 players because it's known to be a very cpu intensive game when more people join. on the source engine in general the performance between medium and high textures has been massivly reduced. before the new rig i used to get unplayable fps spikes with high textures. played portal last night and dam lol was getting crap but playable fps @ 1024x768 with lowest candy. i need a new gfx card :-(
i believe every am2 board supports every am2 cpu? my mobo couldn't recognize my cpu till i flashed the bios now its fine. also with an am2 board you can upgrade to the upcoming phenom quadcore cpus but keep in mind you can't use some upcoming features such as shutting down the other 3 cores when your only using 1 to save power.
i also found out the venice is a good overclocker after i bought my new rig and i noticed your only getting a 4600+ so overclocking your current cpu is also a good solution and probably a better one in my opinion. oh and if you do end up overclocking i recommend you buy some arctic silver 5 cause its cheap and it should lower you cpu temp by atleast 10 degrees celcius.