How To Access Another Computer With Network?

I have one PC and a newly Purchased Laptop.
My PC is running XP Pro and the Laptop Is running Vista Home Basic. I have set up network and have placed both computers on the same workgroup. Both Computers can see each other but on the laptop everytime I try to access the PC through my Laptop I get prompted for a username and password. I have tried to enter the PC's username and password but they do not work. I looked this problem up in the windows help and support and it said something about this being a feature that allows you to access other computers that aren't on the domain. I do not know what that means. So where can i find the password I need?
I would appreciate any help.
Thanks

Go adjust vista users and remove all their passwords.
See if there is a guest account and if there is a password on it too.

Try typing "Administrator" in the username and leaving the password blank.

na doesnt work.
for some reason i now cant type anything into the username box because it is permently set to VICIOUSBOX\guest
Which is strange because i dont have a guest account on my computer

(viciousbox is the name of my pc)