Relax dude, ur so panic, u can't solve by being panic.
Read the gentoo documentation, follow the steps there if u can on how to grub.
http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=1&chap=10Secondly, if u wanna get back ur windows to boot and forget about LINUX, pop in ur windoze CD run the :
FIXMBR and FIXBOOT command and restart ur pc.
If still, u can solve it, please outline ur partition structure: please show ur following output here and the grub.conf. Identify ur kernel name as well, and i can be sure many great linux experts will help u
1. fdisk -l
2. uname -a
3. cat /etc/grub.conf (that's my pc, check urs )
Show all the outputs here ok?