Strange probelm in Kubuntu 8.04

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I am running an up-to-date Kubuntu 8.04 on both my core 2 desktop (2Gb memory) and celeron laptop. Both has VirtualBox (2.02) installed with Win XP guest. All is fine and I love VB, BUT, when I open some programs in the VB, the CPU usage shoots up and stays there (50-60% according to TOP)- other programs are fine, no CPU usage (2-3%). For example, if I open (no activity in the programs) PicBasic IDE or "Registry Care" etc. I get the problem (although XP's task manager reports no CPU usage). I've shut down all the XP services (using XPLite), did a new install with XP home, Pro, no service packs, SP1, SP2, SP3 and all combinations I can think of - still the high CPU usage only with some programs. I even went back to VB 1.6 - same problem on both machines, but VMware Player does not have this problem. PLEASE help!