If you are just simplying moving your connectivity via MPLS VPN then you dont have to make any changes on your side in terms of hardware. So yes your 1721 will work just fine.
Also other things which you need to discuss with your SP before migration to MPLS is.
1) DIscuss with your service provider regarding your topology in detail. You routing requirements.
2) Discuss your SLA requirements, in terms of availabilty, QOS ans other value added features.
And thats it you are set to go via MPLS VPN.
HTH-Cheers,
Swaroop