the program I liked when using XP was called Disktrix UltimateDrefrag but it is not fully compatible for Vista 64 bit YET. They are expecting a new release later this month which I hope it will be. I am not sure but it may be compatible for Vista 32 bit. Anyway, it is not free but it is the best I have ever used hands down, no if's, ands, or buts about it.
With UltimateDrag I could pick where i wanted my files on my hard drives which would make the computer run faster, in my old computer that was a must and I could definitely see a major improvement once I read the instructions carefully and monkeyed with it a few times to get things set the way I wanted. On the C drive I had all Windows folders on the outside of the disc which drastically improved start up and program load times and on my D drive was all my games. I had the game I was playing the most(PR at the time) as the first on the outer most part of the hard drive and when I loaded games, my old computer was able to load maps and get in game almost as fast as some of the newer computers with RAID0 and all that junk.
I know $40 is a lot for the program but was money well spent in my opinion. Oh, for Vista 64 bit, I can get it to defrag my D; and E: drives perfect but not my C: drive. It does not do C: very well at all, uess it doesn't know what to do with the Shadow Copies or whatever and leaves them in place. You can also set archived files and folders that are not used very much which are placed to the inner track of the hard drive(the slowest part). So with the games that have the .bik movie files that are not accessed while playing the game they get moved there, like the ones used for starting up BF2142, BF2, and PR that most people usually rename anyway.