connecting 2 computers together

LLTD allows an XP system to be 'seen' by a Vista system.

I'm not entirely sure that this is your problem (pinging shouldn't present a problem but you never know, it might) - so grab, and install the LLTD routines and see how you go from there.

http://www.microsoft.com/DOWNLOADS/details.aspx?familyid=4F01A31D-EE46-481E-BA11-37F485FA34EA&displaylang=en

you say you can ping FROM the vista PC but not FROM the XP pc, what are you pinging?

Have you set static IP's for both that do not conflict? IE: 10.0.1.5 and 10.0.1.6 and on the same subnet?

Is the XP PC registering a connection (go into Network Connections and check)

Is there a firewall possibly blocking ICMP (ping) or other connections...

Cheers,

Networking using a Crossover cable

http://www.5starsupport.com/tutorial/networking-crossover-cable.htm

How to Configure a Direct Cable Connection with Windows XP Home Edition (PART 1)

http://support.microsoft.com/kb/814981/

File and Printer Sharing in Windows Vista

http://technet.microsoft.com/en-us/library/bb727037.aspx

Click Start, Control Panel, Network and Sharing center, Manage network connections and right click Local area connection and select properties. Untick the box next to Internet Protocol Version 6 (TCP/IPv6) and see if you can connect.

As OM has said check the LLTD responder.

Keep us informed as to your progress if you require further assistance. ;) :D