Upgrading to 64 bit.

You can copy your files (mp3s, videos, documents, save games, etc. etc.) but you can't simply copy your programs back.
You have to properly reinstall all your programs.

What specs does your computer have? There is little advantage to 64bit Windows if you don't have more than 4GB of RAM.

yeah ive got 5gig of ram but when i bought it i didnt realise that 32bit could only use 3gig. also i have a usb 3.0 external harddrive, could i just run windows off of that?

You could. It would be horribly slow.

It sounds like alot of trouble for not much more performance. I would just stick with your current setup.

There are plenty of operational advantages to running 64 bit OSes aside from being able to address more than 4GB of virtual memory. The architecture is expanded from 8 32 bit GPRs to 16 64 bit GPRs which necessitates much less shuffling of data. Longs (64 bit integers) can be stored in a single register. 64 bit Arithmetic is much faster and more efficient as they require only one source register and one destination register which account for 1/8th of the total GPRs available, when done in compatibility mode they require 2 source and 2 destination, which accounts for half of the total GPRs available. Naturally, any resident data needs to be pushed to the stack. The number of XMM/SSE registers is doubled from 8 to 16 as well which allows for SSE operations to be done more efficiently (long mode can use the extra SSE registers, compatibility cannot), also improving floating point performance. NX-Bit which prevents a huge amount of software vulnerabilities, and the aforementioned boost to physical and virtual memory size.

The only drawback to using a 64 bit OS which runs in long mode as opposed to a 32 bit OS which runs in legacy compatibility mode is that there is a small memory overhead due to the larger datatypes and some storage overhead due to the presence of both 64 bit binaries and 32 bit binaries for compatibility. There's really no reason not to use a 64 bit OS

True, but the performance advantage is not that great (10%? 15%?) and non existent when running 32bit applications. (which most consumer software still is)

A complete reinstall is probably more hassle than it's worth in this case.

But you can use all your RAM!

If you do use all that RAM it is worth it!