http://vtun.sourceforge.net/tun/
and follow the installation instructions.
+ If you use OpenVPN on Linux 2.2 or 2.4 or Solaris, you may be
+ suffering from a bug which causes connections to hang under heavy load.
+ The symptoms are very similar to the MTU problems discussed frequently
+ in the OpenVPN mailing lists. But it turns out that this bug is not caused by
+ MTU problems. It's a bug in the tun/tap driver. A patch is provided here:
+
+ http://openvpn.net/patch/tun-sb.patch
+
* Solaris
For 64 bit, I used the tun-1.1.tar.gz source and compiled it.