MBR gets lsot if you install windows... The xp partition you have with data you want to keep can be mounted as an ntfs or fat32 partition after you install linux. Windows wants by default to use the primary channel for installation so that may be teh source of your problems.
So If aI understood your problem correctly. Repartition the C
rive in whatever windows partition you want ii) a swap partition iii )a linux partition.lilo will have to be set up accordingly ,I suggest you use grub it will probably be less messy.