Hey. I'm planning on buying a desktop, but I'm a little confused as to the difference between 32-bit Vista and 64-bit Vista, and exactly what those differences entail.

Now, I think the technical difference is the size of the memory bus. Well, if I'm right, I'm not exactly sure what that means. Does it mean that the address of a memory location can be 32/64 bits long? Or does it have to do with accessing memory? Or both? I could use some clarification on that.

Now, I've also heard that one of the results of this is that a 32-bit OS can only deal with up to 4GB of RAM. However, I've also heard 3 GB. An article I read said that the limit was 4GB, but some computers register less than this because some of the memory is used for address mapping. Is the whether you have a 32/64 bit OS relevant to this space taken up for address mapping?

And lastly, I heard that software designed for a 64-bit OS won't work on a 32-bit. That makes sense, but I'm unclear as to whether software designed for a 32-bit OS will work on a 64-bit.

Please and thank you.

Your info is basically correct.
Memory limits:
32 Bit: 2^32 addresses available (4,294,967,296)= 4.3 GB. Some of this memory space is limited, as you noted, so only 3.2GB is usually available.
64 Bit 2^64 addresses available (18446744073709551616)
17.2 billion gigabytes
This number is limited by the motherboard in question. My ASUS board, for example, will only handle 4 GB.
64 bit computing is more or less the norm now. 32 bit software works fine on 64 bit platforms, but the reverse is not so.
See here for more:
http://en.wikipedia.org/wiki/64-bit

>64 bit computing is more or less the norm now.
I'm a gamer/aspiring game programmer, and I'm getting a computer mostly for gaming. Right now I'm torn between HP and Dell. Dell doesn't offer a 64-bit OS with the model I want, but the HP model doesn't have as good of a video card as Dell. Are there many 64-bit games?

Also, perhaps a more important question, if I'm only getting 4GB of RAM, will a 64-bit OS help me at all? Is that fact that Vista recognizes only around 3.xGB related to the fact that it's 32-bit, or will that memory be used up even in 64-bit Vista?

I'm not aware of any 64 bit games, but it doesn't matter, as 32 Bit software works just fine on a 64 bit platform.
a 32 Bit OS doesn't really use 4 GB of memory, as part of it is already assigned to other functions.
64 bit software is lagging behind, but it will catch up.

I'm not aware of any 64 bit games, but it doesn't matter, as 32 Bit software works just fine on a 64 bit platform.

I know, but like I said, Dell's offering a better video card, but no 64-bit OS, while HP has the 64-bit OS, but a slightly worse video card. So if there aren't too many 64-bit games, I'd prob go with the Dell.

a 32 Bit OS doesn't really use 4 GB of memory, as part of it is already assigned to other functions.

Will that part of it not be used with a 64-bit OS? (assuming I still have 4GB of physical)