some wifi adaptors support AP mode(Access point) but most of them do not. the AR5007 or "Athros" Type wifi's come with a utility that gives a AP mode option. ZyDas is the name of the program that works with these. If you don't have a wifi that supports AP mode then you will have to set up a ad-hoc network and bridge the wifi to wifi so as to use the routers dhcp and not need to configuar anything else.(such as ICS[internet connecton sharing] which rarely works)
how to create ad hoc network
this is a place that will teach you to set up a ad-hoc network in 2 mins. Its really easy with windows 7 , just a few clicks.remember to use regular WEP protection. it is the most compatiable.now after you have your ad hoc network we now need to bridge your Two active networks(IE wifi 1(internet) and wifi 2 (ad-hoc)) to do that i will explain. you need to go back to your network and shareing center and click on change adaptor settings in the left hand side. now you will see your two active connections one that is your internet connection through wifi. and the second will be the ad-hoc network. NOW just highlight by ctrl+click each adaptor OR just drag a square around the two wifi adaptors, right click on one of the highlighted wifi and go to bridge connections. AND your DONE!! afterwards just use the other computer to find your ad-hoc signal, connect and everything will be re routed though the wifi that has the internet and vice versa. whats great is now each computer will have a REGULAR ip address's and dns entries with no further configuarations.
P.S. I did alil research into a more friendler way to make a hot spot without the ad hoc and i found a program called connectify.here looks like it works with MOST wifi's and is a Software AP .No Wifi hardware AP mode is needed. check it out. it might be the option your looking for.