Is there one/which is the best if I need to control XP machines remotely from my MacBook. It would be great if I could use XP to control them as well. Thanks.
VNC comes installed on all Macs (assuming even a vaguely recent OS version), so any VNC client on a PC should work (just make sure you've set it up on the Mac in System Preferences...->Sharing->Apple Remote Desktop).
Chicken of the VNC works well as a client to most VNC servers, such as those you'd install on Windows.
Is there one/which is the best if I need to control XP machines remotely from my MacBook. It would be great if I could use XP to control them as well. Thanks.
Seconded. The RDC client and server are both built into Windows, all you need to do is enable the server (System control panel) and connect using the client.
Timbuktu Pro is the best PC > Mac control I've used.
For the other way around (Mac > PC) like the others have said, the freely available Microsoft Remote Desktop Client for Mac is the easiest option.
Of course, that's much better than what I recommended. I'm still upset with myself that I forgot about it. Works only with XP Pro and Win 2K/NT Server editions, though, right?
I use it nearly every day over a 1Mbit link. Absolutely no issues worth mentioning. LAN speed is a bit slow but I'm not sure whether this is a problem with RDC clients in general or the slowness of Rosetta. You can certainly see the processor utilisation increasing though when RDC is cranked up (i.e. Rosetta overhead).