Is your machine working fine? What will Vista give you that the current O/S does not?
Vista can be a problem when upgrading - it is very memory intensive and should not be considered unless you have at least 1GB of dedicated RAM. If you have onboard graphics the memory for that must be deducted from the system RAM.
Personally I have little love for Vista. For my personal needs it offers no advantages over XP and for my business needs is not yet recommended with much of the software I use.
My point is don't just upgrade because it is available - do so if it makes a difference to your computing experience.