Yes, i tried before. But only for slackware and fedora core 3. For gentoo it's a bit tricky.
Basically what u need to do well:
1. Setup TFTP, DHCP server and NFS server to share ur /mnt/cdrom.
2. Mount your installation cd to the /mnt/cdrom directory.
PXE boot and that's it.
I won't tell u how to do it as it will flow this how guy here unless really have. Well, im actually looking forward to write a how to for this forum. Currently, don't have the time yet. Sorry guys.