We are in the process of upgrading our WAN infrastructure from Frame-relay to MPLS. We have 1841 routers at all our remote sites and a 2851 at the head office. Are the 1841's going to be sufficient to terminate the MPLS connection and run BGP to peer with the PE routers?
When you say MPLS is this going to be a rfc 2547 vrf into an ISP. Which is more likely going to be the case. Therefore you are only replacing one data link for another even though MPLS resides on both L2 and L3. More directly you should be fine with the implementation with BGP. Will the ISP be providing full BGP table or just a default.
Just to clarify, we aren't going to be configuring VRF's on the CE routers... it is simply a connection to the cloud (a replacement for frame-relay) and we are going to receive only private routes through BGP. The routing table should be pretty small.
Based upon your description, since you are doing EBGP to the PE and not going to load the full internet table or partial internet table routes, just your own remote site routes via BGP, Yes, the 1841 should be able to handle the BGP Routes.
One thing to keep an eye on, is the other services that you enable on the 1841 and how much of memory is needed for your internal routing protocols, management traffic, etc. For example, IOS Firewall Features can sometimes be processor intensive, so need to be careful.
I hope it helps.