Is there any way to create an infrastructure wireless network without a router? In other words, is there some way to make a PC behave as a wireless router? Other PCs should be able to see this network as an access point network, not as an Ad-hoc one.
Look at HostAP
Yes you can.
As Peter suggested, look at HostAP. However, it requires a wifi card with specific capabilities. The wifi card needs to be able to run in Master mode, not just infrastructure/ad-hoc modes. Also, you will need to run some flavour of Linux on it.
Why not just use a WAP. Not all WAP's are also routers. Am I understanding your question correctly?