Linux
Try Knoppix which runs from cd and is very good at hardware detection, it is also a great tool for troubleshooting network or PC problems with. If you really want to go for an installed product then Xandros Deluxe will be so easy for you that you won't even realise you aren't using MS. Fedora Core 3 is good but installs as a LVM main disk which is a little annoying when you need to troubleshoot it. SuSE Linux is also very simple to install and use and again can be used from a 'live' cd. My preference is for SuSE which is now owned by Novell but most Servers run RedHat or a RedHat derived OS (Mandrake is also derived from RedHat) so it is useful to know RedHat.
The essential thing is to get Codeweavers Crossover Office (included in Xandros DLX) which will allow you to use Microsoft Office in Linux, you can also run some other windows software with it (DreamWeaver, Flash, Quicken, Photoshop..) which all helps you to feel at home and do something productive.