Windows 7 came out after SPSS 17 was released, so there was no way that SPSS could be engineered to be compatible. Windows 7 does certainly break some software just as Vista did, and Windows XP before that and Windows 2000 before that and Windows NT before that and ...

Whether or not 17 works well enough for you on W7 is an experimental process even though it isn't officially supported on that platform, but don't worry about the risk of wrong results. The computational aspects would not be affected by Windows 7. 32 vs 64 bit could be another issue.