CS would be no problem, 1ghz with a GF3 or so can play that game just fine. WC3 is a bit more intensive, while your main problem is BF1942.
IMO, for high performance in BF1942, heres my "minimum" requirements for smooth gameplay.
CPU - 2GHZ P4, or AXP 2000+
Memory - 512DDR
Videocard - GF4 Ti/Radeon9500
Sure, things could be a little faster if you got a faster processor, but my brother plays BF1942 on his 900mhz P3, not as smooth as my Athlon @ 2.3, but it plays. I'd say the memory and the videocard are the most important factor in all this once you get a CPU around 2ghz.
Keep in mind, this is going to be very expensive.
Lets say, you have 20 computers, each cost $1000 (which is reasonable), that'll be $20,000 in computer parts alone. Not including OS, Games, Desks/Tables, Chairs, Space for rent, connections, power bills, advertisements, internet connection, prizes for winners, etc etc.
If you can get past the initial burdens of the cost, and manage to keep a good userbase or regulars, it could be a pretty profitable.
Good luck.