I agree with Technochic and Carlosdl, more details r required.
Though, I am guessing (because I don’t have clear picture here) this is the problem related to NTLM authentication with Squid. Did u use NTLMV1…. Windows 7doesn’t support NTLMv1 by default. It is working in XP fine but not in Windows 7.
U can try out this….
Start > Run > regedit and find this
Now LmCompatibilityLevel, change it from 3 to 1
Now rebooting the computer.
CAUTION: Before do anything with regedit, it is a good practice to take proper backup of registry and if possible take care about important data !