This and
this will give you some idea of typical wireless router performance and set up. I'm not endorsing these products as there are many other good brands such as Billion, Buffalo, D-Link and Netgear to name but a few.
If however distance and number of walls may be an issue take a look at the 'behind 4th wall' performance of the USR in the first link.
It is worth noting that 802.11g (54Mbps) and 802.11i (Wi-Fi Security) are both IEEE emergent standards and subject to change. In fact both are due for a significant update this quarter. The knock-on effect of this is that the standards can be subject to differing interpretation by the programmers who write the firmware for these devices.
This frequently leads to incompatibility issues between the different bands particularly if you want to run at speeds around 100 Mbps with WPA encryption and MAC filtering.
As such I would urge that you buy the same brand router and pci card as obviously the same company will have thoroughly tested and debugged any connectivity issues amongst its own products. I'm sure we'll hear on here from lots of people who say 'my product A and product B work fine together' but you have been warned because you will only be seeing an insignificant sample on here. The industry consensus is that it remains a risk that's not worth taking unless you have plenty of cash to throw away.
If you don't wish to fit a pci card in your wife's PC you could always go for a USB dongle.
Finally to make sure you are fully secure change your SSID to something like "FLYPRO", set up in infrastructure rather than ad-hoc mode, use WPA-PSK encryption and apply MAC filtering.