Building my own router

I recently decided to setup my own router. It needs to have vpn support as well as ddns. Beyond that I haven't thought much not into it. I was reading some articles and it seems like pfsense would let me do this. I've also seen mention of smoothwall. Does anyone have any experience doing this? I want to be able to use my full bandwidth with the vpn which I currently can't do running it on my router. Some days I do get the full bandwidth if I run it on my computer though. I also want to have very good security. The computer I was thinking about putting it on has a amd e350 cpu, Radeon hd 6310, 500 th hdd, and 4 gigs of ram. Would this set up be strong enough? I had actually planned on building my own but wanted to try it out first with this machine a buddy have me. Any help would be greatly appreciated.

That will be more than enough hardware for pfsense. I'd use that instead of smoothwall since I'm in the process of migrating from smothwall myself whenever I get around to it.

Will the ddns automatically detect any IP change from the VPN? Do you also believe I'll be able to run at my full bandwidth with the VPN?

If it's setup properly it should be fine. I'd imagine the VPN should reduce speeds somewhat but the hardware should be more than enough to get the max out of the VPN.

Do you have a preferred guide you'd use for a newbie? I'm only versed in the Windows environment so I'll essential be flying blind.

I actually found a guide here. My next question is I bought a dual Mic Intel card. Will I be able to use that for in and out or just one or the other? If I can only use it for in or out, which should I use it for?

If it's an intel NIC it should work both ways. My PCI-E 4X dual card was recognized fine.