Can every wireless broadband router be used as an access point?

I'm planning to temporarily purchase a cheap access point, but I found out that broadband wireless routers actually cost less than access points.

I configured a broadband router as an access point in our office. Can I do the same with all possible routers?

My ISP provides a ADSL+2 modem, I want to connect that to an access point and then use Wifi at house.

If the router has both WAN and LAN ethernet ports, you can usually disable DHCP in the router and change the configuration to move the wireless router's network configuration to some unused IP range, then plug your network into the LAN side of the router and nothing into the WAN side to make a poor man's access point.

Wireless clients will connect to the wireless router and receive an address from your main DHCP server (along with the main gateway, dns servers, etc) then communicate with the rest of the network without using the "router" part of the wireless router, as if they had been plugged in to a switch or hub on the network (which is what the LAN ethernet ports are).