The tools you're looking for are:
1. a SERIAL cable to connect your Dreamcast to the PC
2. Serial Slave disc image for your Dreamcast
3. TerraTerm for your PC (Windows)
4. Ripping tutorials (found at
http://www.dccopyworld.com )
5. Various ripping, downsampling, and hacking tools as required (also found at the site listed above).
6. Echelon self-boot tutorial
7. (optional) BIN2BOOT (found at
http://dcxeal.virtualave.net/b2b-cdda-b1.zip )
8. LOTS OF TIME AND PATIENCE!!! It takes most of the day to rip the average game disc, and then you have to extract the files (WinZIP or other GZ capable program), hack them, downsample the Audio & Video files, cut some files out that may not be necessary for game-play (such as foreign language support), and reassemble them into a usable disc image with which to burn to a disc.
If you're lucky, you'll get a usable disc the first time, but odds are you'll need to buy a 50ct or larger spindle of discs to use, because you'll trash a large number of non-usable discs. CDRW discs aren't an option because the Dreamcast in its unmodified state cannot read CDRW discs. You can tweak the laser (via another tutorial) so it will read CDRW discs, however it can lead to shortened laser lifespan.
Good luck in your quest.