Can I use a router with modem if I already have one ?

I have a desktop pc with an internal ADSL modem and a laptop with a USB
modem. Can I use a (wireless) router which has a internal modem without
using IT'S modem and connect using the ADSL modems I already use ?

You could use wireless access point alone to connect your computers
together, but then the one with ADSL connection has to be on for the other
to access internet.
Best to sell both modems (as they are no use with routers) and get ADSL
ethernet modem, router, wireless AP
in one box (or 2 or 3 if you like).
I would suggest Draytek Vigor 2600We, not cheap, but probably the best.
Regards,
Martin