I just tried the sample program from above on Eclipse 3.6.1 with the recent greclipse build and it compiled and ran fine (with the package statement). I haven't yet installed the app engine stuff, hard to see how that would be involved as my test project is just a groovy project with that one bit of code in.
The best thing to do, if you can, is to zip up the minimal failing project and email it to me at aclement AT vmware.com - that would be really helpful. I am 100% sure there is an issue here but if I can't recreate it, it will be very hard to address. Maybe there is something else about the project configuration interfering.
I am also on Windows7 (64bit) which is a difference, but if I could get hold of the failing project that would be a big help.