Remote desktop access

[CwCrei]

Hi folks, :)

Bit of a Linux/Ubuntu newbie, so...

I've got a 6.10 desktop machine sitting on my 100Mbps wired LAN and it's 
working beautifully.

Both my girlfriend and I would like to be able to use this machine's 
desktop remotely over the LAN, mainly from WinXP machines located 
elsewhere in the house (it's sitting on my desk with mouse, keyboard and 
monitor right now, but the plan is to do away with that lot, put it into 
a rack case and hide it away in the equipment rack). I've briefly tried 
using VNC, but have found it slightly clunky and unacceptably slow - as 
a benchmark, there's an 800MHz WinXP Pro box on our network that is 
almost always accessed remotely using Microsoft's Remote Desktop, which 
has performed noticeably faster than VNC to date, and I consider Remote 
Desktop to be only 'adequate' when it comes to speed. VNC has the 
advantage of also offering remote access to my old G3 Mac, but it can be 
unusably slow with screen updates.

So, what's the best way for two people to, sometimes simultaniously, 
remotely access an Ubuntu desktop from WinXP Pro machines, using 
non-commercial software?

Thanks for your help... :)

PJ.