I have been asked to look into this as a possibility,

We would like to set up two links to our ISP (two DSL connections) and
have one for VPN, Email etc and another only used for Web browsing
(via proxy). This will mean 4 network interfaces in the BM box
(Private, DMZ, Public 1, Public 2).

I think this is possible but does anyone have any idea of any issues
that will come up??? Or is it not possible?