“To see a list of all the applications on your Mac that will go phutt when you upgrade to Lion, hold down the Option key, click on the Apple menu, and select System Profiler. In the window that appears, select the Applications entry, which appears under the Software heading.
Click on the Kind column to sort your applications by kind (meaning Classic, Intel, PowerPC, and Universal).
Seek out any that read Classic or PowerPC.
These are the applications that will be incompatible with Lion. (Those Classic applications are also incompatible with Snow Leopard.)”
Another way to do this is to run Xslimmer and let it check what architecture you are presently running. If it doesn’t say Intel then it wont.