the most straightforward way might be to make a bootdiskette which you could use to boot your mandrake after lilo has been smashed, and when you get back to mandrake, re-install lilo and smile
or, the other chance would be to move lilo from MBR to a new, small partition which you would then make active. when you get problems, just make that one deactive and activate your windows-partition, recover it, and then re-activate your lilo-partition (and deactivate win-partition if needed). this way your lilo won't get overrun and you don't need to reinstall it...
I'd say the boot diskette would be the best thing to do. Besides removing Windoze, of course