VMWare and such are very slow
That really depends on what you're trying to do, and what you expect.
be slower, but not ungodly so - as long as you don't attempt gaming or video editing or the like, you'll be fine (and heck, recent versions of vmware have even added DirectX 9 support! - I think there's OpenGL support as well).
If you're running a "normal" guest OS, CPU will be just fine. I haven't tried running anything really performance intensive, but normal usermode stuff should run pretty much full speed - even with a CPU without hypervisor support, usermode stuff can run natively, only with some clever tricks involving kernelmode transitions.
Dunno what happens to intensive Disk I/O, but again - for normal stuff it shouldn't matter. OTOH, for special scenarios, you might even have better speed in a vm. For instance, the install part of both Linux and Windows at least seem
faster to me under vmware. Whether it's because host OS caching is more efficient than the install-time caching of the guest or simply because you can do other things on your machine while installing, well... :-)