Resize your Windows partition. Quite a few tools will do this, such as the commercial Partition Magic or the open source GNU Parted. Try doing a Web search or ask for advice if you've never done this sort of thing.
Convert your disk from MBR to GPT format. I know of three utilities that will do this: My own GPT fdisk under Linux, FreeBSD, or Mac OS X; the standard "gpt" utility of FreeBSD; and the Windows gptgen (which is also supposed to compile under Linux, but didn't for me).
Create a hybrid MBR from your now-GPT disk. My GPT fdisk will do this, as will a tool called gptsync (I know of no central URL for it, but Googling should turn up some download links).