You can happily intermix Apple gear with any other 802.11b standard gear no worries with standard connectivity. I personally mix Cisco and apple gear.
Where you can run into trouble is with the WEP implementations. But as WEP is essentially pretty crap, if you are that fussed about encrypting your traffic, I would recommend running a totally independant VPN software over the top such as pptp something. Sorry I can't be more specific here. I don't worry about encryption at home and probably would use WEP if I needed some as I am not particularly paranoind about it there. However in my office windows enironment, I have setup a L2TP certificate based VPN system. I am not sure if you can get an l2tp client for MAC OS X.
Might have a look though.......