On the XP computer, open "My Network Places" and run the "Network Setup Wizard".
Enter a name and make sure that the box enabling file and print sharing is checked!
You will need to reboot your computer.

On the Vista computer, open the "Control Panel" and click on "Network and Internet", then on "Network and Sharing Center".
Make sure that Network discovery, file sharing and public folder sharing are not on "read only", and that Password protected sharing is off.
Then, Right-click "My Computer" and click "Properties" and under Computer name, domain and workgroup settings click "Change settings". Under "Rename this computer" click Change, and type in the workgroup name you set on the XP computer, and reboot.

On the XP computer, open the Run box and type "\\*name*" where name is the name of the computer running Vista. Drag the files you want to copy to the Vista computer into one of the folders in the Public folder on the Vista computer.

Hi,
Thanks for the help. The last part of your answer was confusing though - i want to access from the Vista laptop to the XP desktop, and what you said in the end is the opposite. Until now i was already able to access files and other things from the XP to the vista. What should i do in order for this side to work? as i said, a simple ping doesn't work.
P.S. in the meanwhile, i will try to follow your steps and see what happens.