If security is a concern for you then WPA/ WPA 2 is definitely the way to go. The PS3 can handle that with no problems.
However, for the moment I would suggest not going with a wireless N router. The specs that manufacturers are using are still in the draft stages and are not finalized plus you would have no speed advantage with the PS3 (it uses 802.11G and 802.11 B ). The router would attempt to go backward to those standards.
Instead, pick up a relatively inexpensive 802.11 G router such as the D-Link WBR- 2310 (currently $60 at Best Buy). You should be able to skip the wireless card in your computer and just use a bit of ethernet cable for its connection and use the wireless for the PS3. If you do want to go wireless with the PC as well, however, the D-Link WDA- 2320 card will work great with the router I suggest.