Mounting one hard drive from another sounds terribly complicated and scary, but it really isn't and is quite benign and reversible. You could just relocate the location of your entire "My Documents" folder (containing "My Pictures") to the new storage location by right clicking the folder, choosing "Properties", and (I can't remember which as I'm not at that machine) on either the "General" or "Target" tabs you will see a "Move..." button. If you click that button, you can browse to the location of your choice and then click "OK". I had already done this on my machine by partitioning the original 80 GB hard drive and moving My Documents to the "Data" partition, but there was not enough space for large graphics and video files. When I bought a new 250 GB drive and installed it as a second hard drive, I wanted to keep as much space as possible for the video and photos, so I had to find a way of keeping my other data files (articles, manuals, etc.) where they were -- away from cramping and fragmenting my OS -- while somehow getting the graphics files to the new HD. I faced exactly the same problem with the original "My Pictures" folder: all programs want to send pictures there, but there wasn't that much space. Rather than manually changing the "save" path each time or manually moving files to an alternate location with more space, I did some research and came upon the topic of mounting one drive from another in Windows XP (works with 2000 also) basic drives (as opposed to dynamic drives).
For this and other solutions and troubleshooting, get a good reference book. I use "Using Windows XP Professional: Special Edition" from Que Publications, available in any Barnes & Nobles.
Before you can mount your chosen extra storage area to the older, limited space drive, you must create an acceptable target for the "mount point". This must be AN EMPTY FOLDER.
I copied all of the DATA (image) files (NOT the ".ini" file or ".DAT" files) to the newly chosen storage area (you may want to create appropriate folders there in advance; see below). Then I deleted the remaining file form that folder. You'll lose the "special folder" status and little photo icon of the "My Pictures" folder, but you won't be using it for its original purpose, and the gain is well worth it. You could just create a new folder named "Pictures" or something similar, but the OS is still going to aim for the original "My Pictures" folder unless it is modified as above.
Mounting is set up from within the Computer Management console (Start-->Administrative Tools-->Computer Management OR Start-->[right click]My Computer-->and choose "Manage"). Click "Disk Management" in the left folder tree, and all of your drives and partitions should show in the right viewing area. Select the new hard drive or a separate partition of the same hard drive by (left) clicking it once, then right click the highlighted drive and choose "Change drive letter or path". This will open a new window, which should show the assigned identifying lette for the drive. At the bottom left of that window, click the "Add" button and then click "Browse". In the browsing window, navigate to the newly emptied "My Pictures" folder and select it. If it is empty and an appropriate mount point, the "OK" (or is it "Add"?) will become active, which will not be the case if the folder is not appropriate. finalizing the choice of that folder closes the browsing window, and now you should see the path to that folder displayed just below the drive letter in the original "change drive letter..." window.
You can do this for more than one user profile (to each user's "My pictures" folder) or to more than one folder within each user profile (e.g., My Movies). As far as I know, there is no limit. I have 3 users on my home machine, so I did this logged on as Administrator for each of the 3 limited accounts. Consequently, the new HD now shows 3 alternate mount paths and points beneath its drive letter when right-clicking the drive in Computer Management's Disc Management section and choosing "Change drive letter or path".
So what do you see when you open or click the original My Pictures folder in My Documents in Windows Explorer (right-click My Computer and choose "Explore" or "Start"-->"Accessories"-->"Windows Explorer")? You see EVERYTHING ON THE NEW DRIVE OR PARTITION. This means (see above) that you should create organizational folders as needed, such as "Bill's Pictures", "Mary's Pictures", etc. In that way, you can select the correct folder in "My Pictures" as the destination for saved files. I hope this helps you as much as it did me.