The problem will be the drivers for the device, The drivers preinstalled on it when xp autodetects it are designed for windows. Try to find some 3rd party drivers for your device if you can this should fix your problem. If it doesnt then let us know, ubuntu has problems with certain wireless adapters where it installs the wrong one as default.
When you installed were you connected to the internet? Is it a new problem or something that has always ben with you as a Mint user?
Can you tell us what wireless adapter it is?
Run this in terminal and post output if you have problems:
lshw -C Network
Other solutions is to install something called "ndiswrapper" and see if you can fix it that way. Note about that though, if it does work you need to remove the adapters you currently have for your usb.
Let us know how you get on or any questions regarding any of the solutions.
2nd gen core i5 : 8Gb RAM : AMD Radeon HD 6770 1Gb GDDR5 : 1Tb 7500 SATA