First, I'm assuming your A2000 came with the GVP A2008 HC+8 scsi board. You need the latest GVP scsi drivers, found
here. Then, download AmiCDFS, found
here.
You'll need to extract the GVP drivers to a floppy by decompressing the DMS archive using XDMS, found
here. This will give you an ADF disk image which can be transferred to floppy with
tracktool.
Each of these tools is pretty self explainitory in terms of usage... Run the program and it'll tell you what to do.
Once you've made the GVP disk, run the installer... Select all the defaults. Extract AmiCDFS to a folder on your harddrive, and run it's installer.
When done, reboot.
Then, modify the CD0: file that comes with AmiCDFS, with the lines device=gvpscsi.device and unit=(the scsi id of the cdrom drive). Place the CD0: file in the workbench:devs/dosdrivers folder... Reboot again, and your CDROM drive should be working!
If you're still having trouble, send me a private message, and I'll give you more precise instructions. I know how it is, since I had to figure all this out myself with my A2000 and A4000 :-D