Your PC should be connected to the router - not the modem.
What kind of router do you have ?
All you really need is a wireless G router and if your laptop doesn't have wireless capability, you'll need to get a wirelss card for it.
A Netgear or Linksys G router (802.11g) would be my first choice and if you need a wireless card for the laptop, try to get the same brand.
You may be able to get a package deal on both. Ignore B, Super-G, Pre-N and anything other than plain G which should be fine for the near future. $30 will get a Netgear on sale and maybe $40 for a Linksys. Cards about the same.