This is a tough one because Vista is notoriously difficult to resize as the bugger keeps a copy of the partition table inside and refuses to boot if the new partition table differs from the kept record.
So you should sort out the Vista installation first, possibly re-install Vista in a partition previously created for it first.
I would probably do the following
(1) Since it is a laptop then there could be a primaary partition wasted for vendor utility, one primary claimed by Vista and another primary used for its system backup and so my Linux must be on logical partitions. One say 10Gb for the Linux and one 1Gb for the swap.
(2) I would leave the vendor partition untouched and use a Linux Live CD to partition something like 30Gb for Vista and may be 10 for the system backup. Make these two "primary" partitions both NTFS type with ID number 7. I would then create my first logical partition of 1Gb for swap (type 82) and then another logical partition of say 10Gb (Type 83) for Linux. I would leave the rest of the empty space for future use. To give a better understanding of how Linux calls its partition I would select terminal mode to run the program cfdisk so that I know hda1 hda2 and hda3 are primaries and the two Linux are named hda5 and hda6 with hda4 named as the extended partition. Apparently a hard disk is a device in Linux and Sata is called sda so if I want to partition a Pata disk the command should be
(3) I will install Vista first and make sure its installer use the two primary partitions as instended. I then check Vista operating satisfactorily before proceeding with Linux.
(4) I shall install Linux on the two logical partitions, select its boot loader to occupy the MBR and expect Vista to be one of the booting choice automatically.
(5) I have the Vista installation CD with which I can restore Vista's boot loader any time should I give up Linux in a future date. Linux boot loader is easier as it can be restored by any Live CD.
I would select the current version Slax or Knoppix for my first Linux and possibly the former as it can give me the root privilage (or admin right in Vista) in the GUI.
I know there is no risk to my data because standard Linux can't write on NTFS partitions (unless installing special program) and therefore can't possibly damage my Vista. Vista on the other hand doesn't support Linux and would not mount its partitions and so I can't even see Linux while In Vista (unless I install special program again).
I am going to find out if it is true that all my MP3, photos, office documents etc can be used straight away in Linux and find out what have I missed all these years.