First of all, RedHat 9 is an older distro. The modems that will work "out of the box" are fewer than Fedora, the newer version of RedHat. I would suggest Fedora Core 3 or 4. Since you are using Windows XP, I assume your computer can handle it ok.
 
Is your system a desktop or laptop computer? make and model?
 
What modem do you currently have?
 
The best way to get a modem working is to get an external Modem, which controls modem functions alone, a "hard modem." Most PCI modems are "winmodems" designed to work with Windows and which rely on the CPU for many functions, rather than being a true "hard modem - controlling functions without relying on the CPU. A good book to start is Linux for Dummies. Don't be offended, it is really a good start. You can usually find good RedHat books at say barnes and Noble, or other large bookstores. Most of the stock they have is outdated, but chances are that a RedHat 9 book will be there.

I have Desktop P$ 2.4 ghz 120 gb SATA HD and 1 GB of ram
Well any brand for serial modem? . US robotics or anyone will work ?
 
I want to start with red 9 and then later on go for fedora .
 
i will check that book .
thanks
waiting for reply
 
 
 

To give credit where credit is due....
 
DapperDan has two that he knows work in Linux. See this thread.
 
I have a Diamond SupraExpress 56k serial modem that worked when I used it. Just make sure that if you find this one, it is the PC version and not the Mac version.
 
If you buy one from a local computer store, other than those noted, ask if it is compatible with Linux. That way, if it is not, you can return it if it does not work.

Try RedHat 9 Unleashed. It's a whopper of a book but it's very through.