If you continue doing the same thing, I bet your account will get banned before you get the chance to withdraw the money. It's not as simple as changing the IP. They can track based on cookies as well and look on the patterns of page browsing. Please bear that in mind.
Don't you ever think that you will not be caught . when CTR goes upto 10% regularly you are highlighted and when you recive clicks from same ip address many times in month you are ready for kicked .
One or Two times is OK...but, DON'T do this again... you have more chances of getting banned if you do more..especially if you're a new adsense publisher. To bury those clicks, get some traffic to your site using social bookmarking sites like digg,ect..and hope some people from other countries click on your ads.
Sticky, if you want a bit more of assurance, then read this http://adsense.blogspot.com/2007/05/accidents-happen.html