The ThinkPad X40 is a great platform to run Linux. The difficulty is finding a distribution which doesn't require a booting CD drive, other than that it is pretty much standard components (except maybe the winmodem).
I know who is TXEric. He is the guy that bought the last version of Windows, Windows XT 2014. He realised that his computer crashed even before the Start menu appeared, swore at him and proceeded to load all his documents on a Russian server before wiping them off from the disk the first time it was connected to the 'Net.
Then he bought a one-way ticket to 2004 at TimeMachine Corp and looked to buy the best Mac available.
Concerning the laptop: you don't really...
Wireless connection will work fine with any Airport card (sold as option) as long as the router is not limited to 802.11a.
Any new Mac will come with MacOS X 10.3.5. If you buy second-hand, you may need to buy MacOS X 10.3 which you can upgrade with a free download to MacOS X 10.3.5.
Don't think there is any chance of a Windows malware mounting your Mac disks and damaging them from inside Virtual PC.
I use ZoneAlarm to protect my Windows installation, and I avoid Internet Explorer as much as possible (http://kmeleon.sourceforge.net for a lightweight alternative for simple browsing). I never ever used Outlook.
No problem so far...
Looks like you want a HD enclosure. If it was for an optical drive I would go for WiebeTech or StorCase Rhino Jr.
You could try the MacPower products, they are cool and quite cheap.
Okay, as planned I put the Nec 2510A in a Prefect FireWire enclosure.
It is totally silent afaict.
I didn't do many test yet, but I found out that the drive is recognised as a DVD reader by MacOS X. Disk Utility doesn't support the drive for burning. I can burn a CD with FireStarter, it works fine using the generic raw driver.
I didn't do any performance testing yet.