I'm quite a bit out of the loop with the latest processors.
 
After installing Vista, I think it's time to upgrade my AMD Athlon 3700+ 2.20 GHZ, get a new mobo, and upgrade from 1 GB RAM to 2 GB RAM.  
 
I have about 400 dollars for all that total.
 
Could you guys give me some pointers as to what are some good-value processors that won't break my budget? And should I get Intel or AMD?  
 
Thanks!

I take it thats socket 939.A dualcore for that is dirt cheap right now and another gig of ram will help Vista as it's a memory hog.

what's the difference between socket 939 aNd LGA 775?

Socket 939 is last gen AMD.775 is Intel and supports core2 which is top dog for now.

Socket 939 = AMD's previous socket, supporting DDR memory
 
Socket AM2 = AMD's new socket, supporting DDR2 memory
 
LGA775 = Intel's current socket, supporting both DDR and DDR2 memory
 
The cheapest route is probably to replace your CPU with a dual core and add another GB of ram.  
 
The alternative is a new CPU, motherboard and DDR2 memory.

I like the AMD X2 5200 or 5600 for good price and performance (& 2M cache as opposed to the lower than 5200 models that sell at good prices (4600 & 4200).  The mobos for AM2 are a lot cheaper than comparable LGA775 boards (M2A-VM HDMI is a fantastic small board with video for real cheap - see DirectCanada or NCIX maybe).  DDR2 memort (AM2 or 775) is unbelievably cheap now - see OCZ platinum rev2 2GB sets.
 
Jo

I remember seeing the 939 X2 CPUs being a lot more expensive than their AM2 counter parts. DDR RAM is also pretty expensive, compaired to DDR2. It might not be too much more to upgrade to an AM2 board. If I wasn't typing this on my phone I'd do a comparison for you.

I say go and get new mobo cpu and RAM. So you can have a better upgrade route from there for later.

 
might be more efficent to either stay where you are, or upgrade pretty much the whole rig

i agree

I'd get an opty 17x or 18x, can still be had relatively cheaply, and another GB of ddr ram.  
 
save the rest of your $, add some more to it, read a bit until Xmas time...  There will be several major changes between now and then.
 
BTW, you didn't mention what GPU you were using, or what PSU you had.  If your GPU is underpowered, a better CPU won't help much if at all.  And if your PSU is an old POS, then you won't be able to upgrade your GPU....

i agree 100% with the above poster (croc), thats all i can say.