Retail Vista has 32 and 64 bit on it.

Its better to go with 32 bit as more support in regards to drivers is around.

Its been proven that 64 bit is faster than 32 bit but again the support is lacking.

32 bit Windows will only allow you to use 4gb of memory where 64 bit allows more.

Home Premium is good enough for most people but if you want all the bells and whistles go with Ultimate.