Nelson
Any Cisco router which has an Ethernet interface for the ADSL, a serial interface for the T1, and an interface for your inside network should be able to do load balancing between the ADSL and the T1 - assuming that you will have a static default route pointing out the T1 and another static default route pointing out the ADSL.
I would suggest that you start by looking at the Cisco 1841 router with a T1 WIC as the router to do what you want.
HTH
Rick
HTH
Rick