Is there a way to enable connections via RDC on multiple computers running WinXP Pro SP3?
Are these computers in a domain where you can apply a group policy to them?
To enable remote connections with a group policy you'll need to enable this policy.
If your systems have the windows firewall enabled you will need to setup an exception for port 3389 in the windows Firewall.
You'll need a value of 3389:TCP:*:enabled:RDP
To login a user will need to be in the group Remote Desktop Users or the local Administrators group.