Last time I had tried qemu+kqemu (on GNU/Linux), it made BSD segfault, kinda like VirtualBox nowadays. But things seem to have changed: I ran the Linuxtag 2008 Live CD Edition inside it (on MirBSD) with no problems at all. Nice, and shows that BSDs can have LKMs.
Now missing: vmxnet source code… or evil BLOB? I suppose the latter.
Unrelated side note: Netcologne is cool, but they suck: you can only change the PTR for your static IP, which you pay 4.90 € per month for, if you’re a business customer. No IPv6 anyway (but SixXS has a new PoP, out of all places in Düsseldorf *evil grin*). And Strato gives gecko2@ two IPs, but only allows the MAC of the built-in NIC (so no bridging to domU or VMs). Why can’t they ever do something not totally clueless? (Okay, I could ask the support… Netcologne support even phoned me back after my eMail enquiry apparently went through their entire house until they could figure out what I need (to mail Fefe, who blocks PTRs like foo-www-xxx-yyy-zzz.ISP), but rejected; Strato support is, from my past experience, hopeless.)