Connecting a laptop to a wireless router - advice appreciated

[#1]

I have an Acer Aspire netbook with built-in wireless capability, and also a Thomson wireless router as supplied  by PlusNet, which is connected by cable to my desktop PC.  I'd like to be able to use my netbook to access the internet but don't know how to set it up: I've searched for information of course but can't seem to find a straightforward step-by-step, words-of-one-syllable guide.  Can anyone point me towards one please?
The Acer is running Windows XP and my main PC has Windows 7.
Many thanks.

[#2]

stage one - on the bottom of the router is the serial number - all capitals, this is also the WPA security caode
Step two go to control panel and network connection, if Wifi is not present add new connection, and on the left "view available WiFi" select yours
then answer the question all should be OK

[#3]

Thanks very much for that.  I'll give it a go.
(Oh, and thanks to whomever moved my question to the correct section.)

[#4]

Quote from: BertCoules

...thanks to whomever moved my question to the correct section.)

You're welcome

[#5]

Quote from: pierre_pierre

...then answer the question all should be OK.

The setup went perfectly, the network was recognised as "PlusNet Wireless: security-enabled wireless network (WPA)" but I can't get a connection.  It times out after a minute or so of displaying Please wait while Windows connects to the "PlusNet Wireless" network.  I don't get any error message so I'm not sure what's going wrong.
Edited to add:
Solved it!  I tried entering the WPA number rather than the serial number and this time it worked.
Many thanks.