Does the 64-bit offer any advantages or rather any disadvantages over the 32-bit version?
For a C2Q or a C2D intel proc (their both 64-bit I think).
Is there any reason to stick to the 32-bit version when the 64-bit version is available? Also will 32-bit version owners get the 64-bit version for free on request or does that have to bought separately.
TIA
answers in quotes
my query:
Will all GAMES play on 64bit as good/better as on 32bit
or Is there any limitation for 64bit for gaming
No limitations as such 
I think 32 bit apps will run a bit slower right? Because they have to run in WoW (Windows on Windows) mode i.e a simulated 32bit environment
If ur currently have anything less than 3GB of memory, stick to Vista 32 bit.
If u have 4GB of memory, also stick to Vista 32 bit. Why?
Vista would be able to use around ~3.5Gig of memory out of the total 4GB in 32 bit OS but in 64 bitOS, it can utilize the full 4GB. Still, the kernel memory and the total reserved memory used by the 64 bit OS itself would increase by ~300MB.
For example, if ur 32bit OS has 600MB reserved for OS and 200MB for kernel, it would increase to 800MB for OS and 250MB for kernel in case of 64 bit OS.
So, u have just an extra of 200MB left for Vista 64 to be used over Vista 32 bit. Ask urself would 200MB make a difference???
Moreover, 64 bit drivers are still difficult to find for any older hardware even some new cheapo products as well. Add to it, 32 bit applications might run slower on 64 bit than on 32 bit, consuming more memory than they would have on 32 bit native OS. Hence, it’s best to stick around 32 bit as of now if u have 4GB or less memory.
If u have ~5GB or more, move to Vista 64 bit coz then u would have around >1.25Gig of extra memory for Vista which would be useful.
If you are going for a new setup, go for x64! It has come of age, and reports are abound on Adobe forums that Flash 10 will ship in x64 version. The beta’s are for x86, but x64 is in works.
And it is high time they release it, and they also understand it.
All the softwares work properly, and with many OEMs switching to x64 as they are shipping computers with 4GB and more RAM now, you will see a much better x64 scenario within an year.
So as an investment and for a new computer, it makes sense to go for the x64.
+1. for the 4Gb explanation. 64bit vista does take up more memory as well, so the gains are pretty much nullified in terms of extra RAM you have.