Is it 5 walls or 50ft ? Anyway it's much less than the 300 feet usually claimed by makers who test these things line of sight and presumably without interference from neighbouring wifi networks.
Before committing him to spending money replacing present card:
1) raise the router above furniture level
2) Experiment with channels (some will work better or worse depending on your environment)
3) If you can detect strong neighbouring wifi, use a channel 5 stops away from strongest.
4) Relocate cordless phone base or video sender etc.
5) Be prepared to move the computer (or at least turn it so your body is not between the router signal and the wireless adapter's antenna.