XP Networking problem

I have lived with this problem for a long time, and figured it would never be
resolved, until, that is ,I found this forum, so hopefully dsomeone can help.

1 Desktop connected to the wirelss router via its USB port
1 Lap Top connected to the same router wirelessly.

All good. As stand alone machines they do everything that they should as such.

However........I cannot get them to communicate and share access with each
other.

On the Laptop I can 'see' the desktop in 'my computer', but it tells me I
dont have permission to access it. Likewise the external Hard Drives
connected to the desktop appear on the laptop 'my computer' but are
inaccesible.

On the Desktop PC , I cannot see the Laptop or any of the external Hard
Drives connected to it in 'my computer'.

I hope this is a clear and concise summary of the problems, I am happy to
give more details if I am told what to give, and any suggestions as to what
is going on would be appreciated.
Thanks.