PPP over SSH is functional and secure but it has major performance problems. See this article for details why:
Basically the problem is that TCP over PPP over SSH (which uses TCP) results in two TCP stacks trying to compensate for errors, which results in really really sloooooow performance.
Use SSH + port forwarding, or just bite the bullet and set up a proper VPN. I just saw this in the store today:
Linksys sells an IPSec VPN router for just over $100! Amazing.