Most companies wait for about a year or so before 'upgrading' to the next Windows OS, mostly to wait for all the bugs to be worked out of it first. I didn't even start using XP until 2006. You can no doubt expect quite a lot of software to no longer work in Windows 7, and especially 64-bit.
If you have 4GB of RAM or less, there is zero advantage to having 64-bit. Although I've heard 64-bit processors can multitask better than 32-bit, even with a 32-bit OS (not sure if thats true, just what I've heard).