I have a config setup that works fine between 3 PCs: 1 vpn server and 2 vpn clients.
Then I tried to connect a wrt54g as a vpn client but I have problems:
I have done "insmod tun" and run "openvpn config.file" and in the log I can see that the certificates are valid, but the tun0 interface doesn't appear.
I do "top" to see the %CPU ussage and openvpn gets a 99% in the initial proccess of authentication and negotiation without any data traffic !!!! 
I think this is a bug in the mips cross-compiled openvpn binary because the same configuration with PC works, and openvpn with static-keys between two WRT54G works also.

Any body running openvpn in WRT54G with Certificates instead of static-keys?
Any help?
Any idea?

How high is your router loaded ? In fact openvpn is not requiring too much CPU time if you don't transfer files on the tunnel. I don't think the tun interface should disapear on high loaded router, and I think there must be a missconfiguration causing this issue.

Well, the info in /proc/loadavg starts at 0.03 and then raise upto 1.00 in less than 2 minutes
With "top" the CPU usage for openvpn is 99%.

I don't think about a wrong configuration because I have the same setup with i386 PCs and it runs fine.
I really don't know what could be the thing that cause this behavior.

Any idea?

Well, "works here", so I wouldn't name it a bug in the cross-compiled binary.
Do you start openvpn in init scripts, or do you do it manually?

Hi, thanks for your answer.
Actually I have moved the VPN to a PPTP-Server so I can connecto Windows Clients easilly. But I'm still interested in OpenVPN.

Shining, when I run the OpenVPN client in the WRT54G, I did it manually. Can you show me your config setup and openvpn version or links to the ipkgs?

Thanks a lot.