I have just went through that same pain. Some of the eariler versions of the PIX OS on the 515 had a bug. If you have it under warrenty or what not you can call Cisco and they will talk you through it, but since you probably don't want to go down that route, Cisco can't provide you with much help.
Here is what I did. I static mapped the VPN network on the outside interface of the firewall
static (outside,inside) 192.168.0.50 192.168.0.50 netmask 255.255.255.x
What you can do to test it is turn on the debug command for the icmp
debug icmp trace
With the debug on, the firewall will display the reply command since it probably isn't set up so that it can be displayed on the computer.
After you verify that you have connection with the ping, then all you need to do is create acls for whatever you want to permit in, such as telnet.