Is the modem a software modem or a hardware modem ? I suspect you are using a "soft" modem and this might be part of your problem. Most modems are described as Software modem, soft modem, Winmodem or something similar. This means that they need windows in order to be able to run.
If you are using a software modem then changes made to Windows, (like re-installing after reformatting the hard drive). may affect the modems performance. If the windows drivers were set up differently then you will have a problem, (such as lower speed).
The alternative to a "Software modem" is a "Hardware modem". The difference between a Software and Hardware modem is that a soft modem needs to interact a lot with the processor and the Operating System. A software modem slows down the processor and will only work with WIndows. A hardware modem has minimal interaction with the processor and will operate on any operating system.
If you find you cannot use this modem to run Linux then this is a giveaway that you are using a soft modem.
All soft modems have a high degree of interaction with the processor and OS and even though they are rated at 56K they cannot deliver 56K. This is because of the overhead of interacting w/processor. They are processor and OS dependent.
Hardware modems are not dependent on the operating system. They typicaly have 80% less interaction with the procesor. Hardware modems rated at 56K are much faster than their soft equivalent.
Hardware modems are always faster than software modems. A 56K hardware modem will not deliver 56K because it too has some overhead but I can say that the one I installed on my PC at home will is giving me 44K right now.
I have a very noisy phone line, my neighbour is a CB radio enthusiast, and the line quality was tested using a special meter. On a scale of 1=low to 10=high my line tested at 3.4. On a soft ISa modem I had lots of random disconnecs. Up grade to a soft PCI modem stopped the disconnects but was slow, the "cure" for me was a PCI hardware modem that I bought from ebay for forty dollars.
Hardware modems are more expensive than software modems and unless you specify otherwise most stores will use soft modems. When you bought your PC did you specify a hardware modem ? If not then you almost certainly have a software modem installed.
Most hardware modems are ISA and this slows them down a bit. They run on the ISa bus which is slowerr than the PCI bus.
I would buy and install a hardware modem that runs on the PCI bus. If you like you can leave the software modem in the machine then you can try the Hardware and Software modems side by side, unplug the phone cord form one, plug it into the other one rebbot, reconnect and and see which one performs best and gives the best speed.
If you have any questions send me an email eugeneokeeffe@hotmail.com
Hope this helps
Eujay