Hi there and
to the forums.
You will indeed need wireless cards in each of your systems.
These do not cost much and I always reccomend you go with an internal PCI card than the USB wireless sticks as I have known them to not be as reliable.
Most PCI cards will do the same job so it doesnt really matter what you go for here. If you want to be sure, just go for the same make as your router.
Many people here like the Linksys WRT54GSUK router.
Available here:
http://www.amazon.co.uk/Wireless-G-B...4216202&sr=8-1
Do note that your current modem will have to have an ethernet port on it to connect to the router.
If it does not, you will need to look for an ADSL router.
The reason I recommend this one is in the event you change to another ISP, you will be able to use it.
You will not have to install any additional software to your PC's unless they require drivers that come with your network cards.
The thing about Wifi is that although it will work most of the time it does depend on the surroundings, so you can't guarentee a 100% connection rate.
You should be ok most of the time though.