this is my dp...
I assume that the printer is connected to the desktop PC via USB, in which case sharing documents with another computer (the laptop) and sharing the printer (with the laptop) are very similar problems.
Each of the computers should have a name, it is likely that it is something set automatically, although you may have chosen it at some point. You need to find the name of each machine.
start -> run ... in the box type 'cmd'. this will open a command shell. At the prompt type 'hostname' and press 'return'. Each machine should respond with it's hostname.
Now, assume your desktop is called 'bumpy' (like mine).. on bumpy, open 'my computer' and, in the bar at the top type '\bumpy' this will show you what has been shared. If, on the laptop (say it's called 'laptop') you type '\bumpy' then you should see what is being shared by the desktop.
The main problem with this is that you may not have anything shared from the desktop. So, you will need to right-click a folder that you want to share and select 'sharing' and then 'share this folder'. You should now see it when you look at '\bumpy' (from either machine).. there is a similar sharing process for printers.
The next problem is that XP likes to enable its firewall, this may prevent communication between the machines - so, find the wireless network connection (right click 'network places' and select properties') and right-click and select properties of the wireless connection (or, on the desktop, this will be the wired ethernet network connection) you should see an option to disable the firewall.
Of course, leaving this disabled when on other networks or when connected to the internet without another firewall (hopefuly the wireless router has one of its own to look after you) is very dumb, so proceed with caution (maybe even unplug from the internet while testing)
All of this is a huge pain the the arse, which is why you will end-up giving up and getting someone to set it up for you.
that is all.
bob out.
Your connection to the internet via the wireless router