Connectivity

I have a dell dimension, operating XP Pro, which is connected via
ethernet lan 100mbs to an SMC Barricade G wireless router, strange
way to connect you might think, but I did have another desktop in the
house which was connected wirelessly and intend to do the same in the
future, and the router is six inches away from my current pc which
does not have a wireless adapter, hence the wired connection.

The problem I am now having is that I bought my daughter an Acer
Aspire 9815WKMi laptop, operating Vista Home Premium, and has an
Intel 802.11g wireless adapter installed and cannot get it to connect
to the barricade router without apparently kicking off the desktop
connection.
Even then, it say's that it only has limited local connectivity and
cannot connect to the internet.

Thinking that this might be a router problem, I took the laptop to
another location with a lynksys wireless router to no avail.

With my other pc's operating XP Pro I just look up available
networks, select the SMC, enter the WEP passphrase, the router
automatically allocates an IP address, 192.168.2.200 for the first
one and then 192.168.2.201 for the next etc. and everthing connects
without any problems, giving full internet connectivity to all pc's.

As the Acer is operating Vista, I am unsure of the correct procedures
for connecting to the router, although I have tried over and over
again to go through simmilar procedures to XP, and followed any
prompts etc. without any success apart from the aforementioned
problems.

Please can anyone help me to, firstly, undo any changes that I might
have made, to return any settings to their basic state, and let me
have a basic, hopefully foolproof, procedure for connecting this
laptop to my router.