I found out about VirtualBox from a post on osnews.com which linked to a review. It's an free software (GPL) virtual machine that runs on Linux and looks quite spiffy. Benchmarks in the review suggest about a 2x slowdown on a mixed CPU/disk workload. I could live with that if meant I didn't have to boot into Windows any more. Note to self: try installing this!
Meanwhile, KVM (Kernel-based Virtual Machine) seems to be gaining momentum, but it requires hardware-level virtualization in the CPU it runs on. Maybe I'll buy a real computer this summer and I can try it out.