Hello, Alex,
FreeSWAN and OpenVPN are similar only in that proper configuration and deployment results in similar functionality. If you are using properly signed certificates (not self-signed) with your current setup, those certificates will likely function with OpenVPN as well.
Once you have a handle on how you want OpenVPN to work in your environment, you can easily deploy it on the same system that is currently serving IPSec connectivity and migrate your road warriors away from IPSec. Since you're not a VPN wiz, I would encourage you to do your configuration testing on systems other than your production VPN concentrator. OpenVPN will make modifications to your routing tables, so you will want to have a handle on what it is doing relative to what you currently have before putting those two cats in the same closet.
Assuming you've thought out why you want to migrate, I find OpenVPN to be a much less constrictive system to work with while providing a good, strong crypto framework for protecting data and linking remote sites together.
Let us know if you run into any roadblocks after you've gotten your initial configuration in place. Most questions can be answered from the documentation page (
http://openvpn.net) and there are also the openvpn mailing lists.
Good luck!
Regards,
Stephen
