1) Connect the crossover cable to both computers, internet connection will drop.
2) Set the computers network cards as follows:

Laptop:
netsh interface ip set address "Local Area Connection" static 192.168.0.2 255.255.255.0 192.168.0.1 1

Desktop:
netsh interface ip set address "Local Area Connection" static 192.168.0.3 255.255.255.0 192.168.0.1 1

3) Check for connectivity.
From laptop: ping 192.168.0.3
You _MUST_ receive replies, otherwise something has gone wrong.

4) Since you've already shared the folders in question, you now just need to access these shares.
Just open up "My network Places" and browse for your shared folders. 

If this doesn't work do the following:
Type this into your laptop's File exlorer address bar (you can type it into Internet Explorer's address bar, too):
\\192.168.0.3
There you will see the folders that you've shared on the desktop.
Viceversa would be typing \\192.168.0.2 in the desktop's explorer address bar.
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To go back to the settings you had before all this, on BOTH computers:
netsh interface ip set address "Local Area Connection" dhcp

Then connect the cable to whatever computer you prefer.