In order for OSPF to work, your ISP's would have to participate. I would forget about the use of a routing protocol. I would like to add I would never try to do what you’ve been asked to.
Does the web server reside on the same network as the users? If so, you would have to use a route-map statement to make sure the web server went out the T1. You would also need to have three default routes for the Internet, all with the same cost. The downside to this is if a DSL line went down, the router would never know. It will use if the VLAN is up or not, so if a DSL line goes down, that VLAN will still remain up. With three DSL lines, that would give you a 33.3% drop packet rate. If you could put DSL WICs in the router, which would do what you are after. Lastly, there would be no way to fail over to the T1. A routing protocol is the only way and you won't find a DSL provider willing to do it. I would go to your boss and say his idea is not feasible with the equipment on hand.
If you could deal with two DSL lines, you could do the route-map for the web server to use the T1. For the two DSL lines, you could use a Linksys router, like the RV042 or RV082, which allows the use of two Internet connections. You can set one as primary and the other a backup, or do load sharing. Then you would just need one default route for the users. If you really need three DSL lines, you could do the above, but with two Linksys routers with two default routes. This would still leave you with a problem if the DSL line on the Linksys with just eats goes down, but with a 50% drop rate instead of 33.3%. In order to get around this, four DSL lines could be used, two on each. If one DSL lines goes down in that scenario, packets would not get dropped. To go one-step further, I would look at two DSL providers, each will provide two DSL lines. Linksys router "A" would have one DSL line from each provider; Linksys router "B" would be setup the same. If one provider has an issue, you wouldn't get the 50% drop rate as you would if one provider was on one router.
May I ask how many users and how much bandwidth you really need? Is Internet that really important? Is cable offered in your area? Some cable companies are offering 6 or 8 Mbps. You could getaway with the above setup, but one cable and one DSL. That would provide a higher level of availability then just DSL and guarantee different providers and paths.
