Find some cash and invest in extra memory for your mac. I know it's probably not the tip you want to hear, but honestly, it'll save you frustration in the long run. Apple ships these babies with way less memory than they deserve, and charges an arm and a leg for an expansion. I had a Mac Pro (quad-core Xeon) crawl to a halt until I got some real memory in there.
Another tip is to get a decent keyboard and mouse. Don't trust Steve Jobs with that "single mouse key for everything" crap. It works for ichat, not for real programming. Get yourself a real keyboard and a real mouse with multiple buttons. Configure your middle scrollwheel button to open expose or whatever it is that shows you all windows. Configure your fourth button for magnification.
Also, from your description it sounds like you don't really know what it is that you want to develop. If you're doing mac-specific things, get used to XCode ASAP and lose the rest. If you want to be doing windows programming, not sure why you would use a mac. If you want Java, you have Eclipse, you're ready to go.
