To use SLIP/PPP, you need a computer, modem and telephone line. This may sound like nothing more than what you already use for normal host dial-up access. This is probably true for many users. However, there are some points to note.
For the PC running Windows 3.x, a low-end 486 with 8 MB RAM will be good. You'll probably want a mid-range to high-end 486 with 16 MB RAM to run Win 95 and/or OS/2 comfortably. These are recommendations for "comfortable internet surfing"; In practice, you may be able to work with less powerful hardware.
Here's a simple test to determine if your modem already passes clean 8-bit
data and uses hardware flow control: Use your communication software to
dial into a BBS or online service, or anything that lets you transfer
files. Try uploading a binary file (eg., compressed ZIP archive) of
non-trivial size. Do whatever is necessary to determine that the remote
end received your file correctly. For example, the command unzip -t
<filename> will test the correctness of ZIP archives. Then,
try downloading a binary file (you can use the same one you uploaded).
Again, do whatever is necessary to determine that you received the file
correctly.
If both uploads and downloads are fine, chances are that with your current modem and serial port settings, you already have a clean 8-bit data connection that uses hardware flow control.