the real advantages of having a dual core cpu will not be fully realized for just a bit longer. The new Winblows OS will not require a multi core cpu,...but will have optimizations to utilize one. In addition, gaming is moving towards multi threading and in about a year most games will run better on a multi core cpu. What you need to ask yourself is this.
How often can I afford to upgrade? If you will have no problem ponying out some dough in a year to jump on the multi core bandwagon then saving some cash now may make sense. The Intel camp looks nice now,..CoreDuo finally gives them the performance crown but Intel is too well known for jumping ship on socket layouts. AMD on the other hand,..may not have the top dog in architecture,...but the AM2 socket has been guaranteed to be around for a while. This means that if you move to an Intel based mobo that this time next year you may only be able to upgrade to todays top Intel CPU,....but if you go AMD you should be able to utilize thier next gen chip.