I successfully managed to control a rc tank serially with a GUI using prcoessing(on my pc). Now, I want to control it using wifi but I'm not really sure how to approach this. Any help would be greatly appreciated.
Here's an example using a modified Linksys WRT54G router:
Now, that's based on a PIC microcontroller, but others have done similar projects with the Arduino (just look up "WRT54G arduino serial" or similar); you should be able to work out things from there, given how far you've already gone.
Also - you could substitute in a wifi shield or similar instead of using a hacked router; so that you have the most memory available, you're going to want such a shield to have an intelligent wifi chipset on it (that will handle the heavy IP stuff, instead of forcing you to use a library that takes a ton of SRAM and such doing the same on the Arduino) - so look carefully for such a board if you decide to go that route (basically, the more expensive the wifi shield, the more likely it will be one of those chipsets - but do your research carefully).
Thanks for the reply. My micro controller has built in wifi (digix). It's 100% arduino compatible and the last step I need to do is to figure out how to send data from the processing GUI to the arduino using wifi. I'm wondering if there are any specific libraries that could be used to accomplish this.