as above - Any ethernet cable will do. It doesn't matter if it is a crossover or a regular cable. Apple has used clever NICs (ethernet card) in the powerbook range that auto detect if the computer is connected to a network or directly to another computer.
If that doesn't work straight off you may need to set IP addresses on both machines as Microsoft does not implement the rendezvous technology.
To do this:
Mac: Open System Prefs, open network, select ethernet. You want to configure manually. In the IP address type 192.168.1.10 you can leave the other fields blank (subnet mask should already be 255.255.255.0)
PC: open the network control panel, double click the ethernet controller icon, select the TCP/IP item and click properties, select the radio button that says configure manually, enter 192.168.1.11 in the IP address field, click apply and ok.
Your computers should now be able to "talk" each other. To double check on the PC select run from the start menu and type "cmd" then type "ping 192.168.1.10" (note thats the IP address of your Mac) in the dos prompt. You should get back something that resemble some thing like this
64 bytes from 192.168.1.10: icmp_seq=0 ttl=64 time=0.303 ms
If it says timed-out or unreachable then something's wrong.
You should now be able to connect via file sharing etc as normal.
Just a side rant/note. Why oh why didn't Microsoft implement the auto-detect crossover NICs in the XBox? That would have made life a little easier...
Any problems post back!