Implementing redundancy on 2 FastEhernet Interfaces on 2800

I believe there are multiple ways to do this.

You can set up a static route on your 2800 and the internet router to default all traffic to fe0/0 and a higher cost floating static route to send all traffic to fe0/1. (Or if you are using a routing protocol then you only need to make sure that the routes to the other interface are of higher cost)

Or load-balance - You can either use eigrp between your 2800 and your internet router and do load balancing across both (so even if one goes down the other will still be operational and you'll have 2x100mbps). Another way is to just use cisco express forwarding on both interfaces and the router will load balance across both.