So I gave my uncle Mepis, he loves it, but I had to get a serial modem for his dial-up account. Its over an hour drive so most of our trouble-shooting has been done via telephone, but we cannot get the modem to connect no matter what we try!

We did these two options:
wvdial help (we had to remove both Init lines, dunno why), and kppp help but neither want to actually connect. Both dial, both talk a bit, but kppp cannot start the "pppd interface" (!?) and wvdial has a "sketchy connection" or something, and a "difficult time handshaking" (or something similar, as this is from memory from our recent conversation)

Any ideas out there!? Thanks LQers!

Try Kppp more than once. I've found that it will fail the first time and then work fine.
On a different forum, whirlpool.com.au, there is a post similar to yours where the poster finds that he has to always try his kppp twice after boot up for it to work properly, he too is using Mephis.

try this -- backup whatever you have done with wvdial and then
let it figure out it's own settings
then just add ISP's phone number, login name and password into the /etc/wvdial.conf file