I've not tried this myself, but we use these Yawarra boxes (http://www.yawarra.com.au/hw-alix.php), which are slightly more expensive than you may be looking for, but could be worth looking at. We've used them at work a couple of times, and if I remember correctly we had success installing Debian Lenny on them, but Ubuntu I think had a kernel issue.
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Oh no, didn't you hear? Linux isn't safe any more either :-)! http://www.downloadsquad.com/2009/10/27/how-good-is-wine-at-running-windows-software-on-linux-good-enou
But it's OK, most of those spyware protection programs are available on Linux as well! The link above shows how to install Windows Police Pro!
I've not tried this myself, but we use these Yawarra boxes (http://www.yawarra.com.au/hw-alix.php), which are slightly more expensive than you may be looking for, but could be worth looking at. We've used them at work a couple of times, and if I remember correctly we had success installing Debian Lenny on them, but Ubuntu I think had a kernel issue.