There is a lot of info on calendar sharing in Outlook's built-in help. It looks to me like the advent of Office 2010 will mean web sharing of Outlook calendars will be discontinued; you'll still be able to share them via Outlook 2007, but only if both machines have a legitimate installation of the program.
I may be wrong, and may have therefore wasted my money, but I did a lot of research on syncing Outlook across computers and SYNCING.NET seemed the best way to go. In practice, it has worked flawlessly.
One other thing to consider is to use a PDA to sync the 2 machines. If you buy a cheap 7-compatible PDA (or smartphone, for that matter) and sync it to one of your machines, you can then connect the PDA to the other and sync the info again, putting all 3 devices in sync. I imagine you can get a PDA for not much more than GBP110, so it rivals SYNCING.NET for cost, plus you have a new gadget to play with