If you're mailing files between windows system then you are really doing things the hard way. Windows will let you "share" a file, a directory (folder) or even an entire disk partition. You can make the share read-only or read-write, and you can control who has access (either by password in Win98 or by password and user account information in XP, they work somewhat differently but do interact). I would suggest that you learn to do this before trying to get Knoppix to share files with XP.

Knoppix has tools that let it network and share files with XP. Sometimes this can be simple to set up, sometimes not. Unfortunately, it looks to me like Windows has done things to make sharing files between Linux and Windows slower than need be. The way I have found that works best for me is not to use the Windows file sharing logic at all, but rather to use FTP. I start a FTP server on one side and use an FTP client on the other to move files back and forth between systems. This makes for much faster transfers, particularly with lots of files or large files.

There are plenty of good windows FTP servers out there. I would suggest looking at Filezilla, although there are others and whatever you like can be a good choice. I believe that the 5.0.1 DVD now has a FTP server on it but I'm not certain of that as I have not used it, I only use a FTP client on the Knoppix side. For that Konquror (the browser window that starts when KNoppix starts) is a perfectly fine FTP client, although there are other choices there too.