Yes, you don’t have to run the system on a router. All you need to do is to install Coovachilli and set the chilli parameters manually. Coovachilli is an open source captive portal or wireless LAN access point controller. Binary downloads are available for Redhat, Febora, Debian, Mandrake and OpenWRT. Coovachilli is an ebuild in Gentoo and compiles under FreeBSD. Source code under GPL is available for other platforms.
Another option to operate a hotspot on a PC is to install RouterOS on it (its the operating system of Mikrotik routers but it can be installed to a PC). Please note that you need to have a Level 4 license or higher for hotspot functionality.