If you are asking should you wait until 2008..... that means you think you can and your computer will do untill then... So maybe you have already answered your own question.
If you have to (as in want to for whatever reason) upgrade now or in near future, then if you feel the need and have the dosh and inclination, then plan to upgrade say in three months, and spend that time deciding what you want your computer to do, and what kit will best suit that objective.
It will always be cheaper and faster next (whenever Month/ Quarter/Year)... and often there is no "best time", just "your time". I have been pondering upgrading for a year now, and have changed my plan fundamentally several times during that time, with ony a couple of exceptione (e.g. case - and three days after I buy a Sonata 2 for my daughter's new PC and a P180 for mine, the Sonata 3 and the P182 are launched).
There is some very good stuff available now, propably the best ever, but there is always "jam tomorrow".
Good luck!