Wireless or cable

I had my WinXP connected to my modem and my Win7 connected wireless.

#1- I'm wondering if I should leave my Win7 connected via wireless or whether I should connect it (Win7) directly to the modem?
Would the Win7 run faster if I connected it (via cable) directly to my modem, or be more 'secure,' etc.?

#2- I believe I can connect up to 4 computers directly to the modem (via cable). Is that correct?

I hope I explained this correctly as I am not too sure of the terminology, etc.
Thank you for any help.