Performance issues (reproducible) Parallels 6 and Java Applications in OSX

I'm using Parallels 6.0.11992 on 10.6.6 - I had this issue with older versions of both OSX and Parallels as well - and I'm running Windows 7 32bit corporate set up with 1 CPU, 1GB of RAM. I'm running it on a mid 2010 iMac, 3.06GHz C2D, 4GB Ram, 7200RPM HDD

Windows runs well, if I don't run any Java Application in OSX. The Java Applications (mainly NetBeans) run very well, if I don't run Parallels. Running both together makes the machine almost unusable. While CPU and RAM usage stay low, either Parallels or Java seem somehow to cut off HDD performance.

This goes so far that the Mac can't be used at all for minutes sometimes. Any advice would be much appreciated.

--Martin