two ways you can check if you have ntfs:
1) if your windows files are mounted into Xandros, go to that mountpoint (/windows on many machines), right click and click properties, it should give you information about the drive including FS type.
2) if you login to windows, do the same: right click on the C: drive, click properties, it will be listed under "Drive Format" or something similar.
You'll either have FAT16, FAT32, or NTFS. FAT is easily writeable from linux, NTFS not so much. As for being infested, it's not necessarily true that anything needed to be done to your system. Check your router / firewall / server for an open port 25 (the SMTP port). If that's open and you have an SMTP server running on your machine(s), they can just specify your IP as the host through their mail client and voila... mail coming from your machine.
Solution would be, tell the router not to allow port 25 access from outside your LAN, or just turn off your SMTP server.
Whatever the problem is, good luck! We'll all be glad you're shutting down a spammer, if only temporarily!