some questions for a start:
1. i assume is it 2 partitions on on hdd? (not two different harddisks for the two operating systems)
2. i assume you did use mbr partiton scheme?

notes
1. if osx would reside on a seperate hdd, esp. an external usb one, it would be hassle free to install and
experiment. and one can use the bios bootloader. worth a consideration if u got a chaep external disk
lying around.
2. guid would brake win xp when used on same drive and can not incorporated
in vista bootloader.
(and guid bootloader is broken on r2, has to be fixed manually)
so mbr is the way to go (beware, diskutil sometimes has guid as default)

did you read:
http://osx86leo4all.wikidot.com/how-to-s#toc5 (with the solution winlinmac mentioned)
making partition bootable: http://osx86.wikidot.com/known-issues#toc3
reinstall the efi bootloader manually, see: http://osx86leo4all.wikidot.com/how-to-s#toc5

btw: can you boot into osx if you use the dvd to boot?

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Leopard 10.6.5 | Core i3 | Gigabyte H55M-USB3 | ATI 5770 | Coolermaster Cosmos