this is a subject to which we will return again and again over the coming months.
The first thing to appreciate is that a 32bit machine will continue to function perfectly well, regardless of the coming of 64bit computing. Nothin will happen to change that overnight, and software companies will continue to produce 32 bit products fore as long as there's a substantial market - which I suspect will be for quite a long time to come. The development environment for 64bit programs is almost identical to that for 32bit and it will be relatively easy to produce versions for both.
By all means buy into 64bit technology if you feel inclined - you can get an evaluation copy of the 64bit version of WinXP now, although beware - it will only run with an AMD 64bit Opteron or 64bit Athlon processor, the 64bit Intel Itanium processor isn't currently supported.