Going back to 32 Bit?

Yes.

Yes, it is.

Here you go, this wikipedia page presents a good amount of information
64-bit - Wikipedia, the free encyclopedia
There is a section discussing differences between 32-bit and 64-bit.

32 bit software does not take advantage of the the 64 bit processing power. 64 bit computers will run 32 bit programs; but they will not run the old 16 bit legacy software.

If it were me, I would opt for the 64 bit Windows installation if my computer and hardware were fully capable and I would install 64 bit programs when they are available. You may have some driver problems with a 64 bit installation, which you can correct. If my computer and hardware were marginal, I would opt for a 32 bit installation.

Oh and if I install windows 7 ultimate 32 bit on a 64 bit pc will it run just as fast as on a 32 bit computer or slower?

That is a hard question to answer since "fast" depends on the processor speed, RAM, and hard drive speed.

In addition to what Carl has said, an important note is that 32-bit will not allow you to use more than 3.5GB of RAM, even if you have more installed.

Very good point, Fred. I don't think of that because I a running 32 bit with 2.5 Gb of RAM.