is usually a niche that is difficult to fill.
One can still find external modems if you [link|http://item.express.ebay.com/__Modems_External-Modem-56K-v-92-Data-Fax-Voice-New_W0QQitemZ6885982449QQihZ013QQptdnZModemsQQptdiZ263QQcmdZExpressItem|look around].
Ubuntu and many other distros use [link|http://open.nit.ca/wiki/index.php?page=WvDial|wvdial] as the back-end well - just like PuppyLinux. Some tips on using a modem with ubuntu is [link|http://www.ubuntugeek.com/setting-up-dial-up-connection-in-ubuntu.html|here]. The magic seems to be in the wvdial.conf file. Apparently if [link|http://www.die.net/doc/linux/man/man5/wvdial.conf.5.html|wvdial.conf] can't find the modem, it's either due to it being a WinModem or due to an [link|http://open.nit.ca/wiki/index.php?page=WvDialFAQ#toc21|IRQ conflict].
I haven't been able to find a database of supported modems, but maybe the view is that it's not necessary to have such a list. Apparently all true external modems should work unless there's a conflict. True modems are, or emulate, standard devices and don't need "drivers" the way brain-dead WinModems do because they have their own on-board intelligence. True modems should Just Work (TM).
As to why it works with Puppy and not with others - I assume it's due to someone with Puppy actually taking the time to make sure it works. :-)
This sounds like a business opportunity, Ashton. :-)
One could also try [link|http://www.fx.dk/injoy/|InJoy]. I used it for years on OS/2 and it always worked very well. It was well worth the money to me. There's a (RedHat) Linux version,too. It's $35 for the Basic version (1 year free upgrades, best effort support). The downloaded version is fully-functional. Paying the registration fee enables other features, and makes use after 30 days legal.
HTH a bit.
Cheers,
Scott.