Here's a quick and easy fix to the common problem of getting lips textures to line up on models that share textures such as V3/SP, Sara1/Sara2, etc..
I will be using my freebie texture Galina for Sara1 as an example here because I know its lip texture does not line up correctly on Sara2. The upper lip comes much too high on Sara2 while it looks fine on Sara1.
Alright so we are going to open the head texture in our paint program of choice (Photoshop, Paintshop, Gimp, etc.).
Now choose your area selection tool and make sure it's on rectangle selection.
Now select the area around the lip area of the texture.
Invert your current selection. Now everything BUT the lips should be selected.
Add a new layer and choose your paintbucket or floodfill tool and with the color WHITE we're going to fill in the selection we've created.
Deselect your selection area.
Now Save As… to a new file. MAKE SURE you Save As… so you don't overwrite your original texture.
Now with our lips cut off and save as a new file we're going to remove the lips from our texture.
Select your clone or rubber stamp tool, then pick areas of the head texture that are the same color as the area AROUND or NEAR the lips.
Clone or stamp over the lips until it's smooth and blank in the lips area of the texture.
Now Save As… to a new file. MAKE SURE you Save As… so you don't over write your original texture.
You should now have 3 textures; 1 original head texture with lips applied, 1 with just the lips in the center of a white texture, and 1 with head texture with the lips removed.
I use MAT Pose Edit, which is an great free program for creating MAT and MOR poses. You can find it here: http://koti.mbnet.fi/~ilaripih/MPEHome/.
I'll be explaining how to create new MAT poses for the textures we've just edited, if you have another method you are more comfortable with free feel to use it. The follow instructions assume you have a bit of experience with MPE or MAT poses in general. If not there are tutorials on how to setup a MAT pose from start to finish on the MPE site.
Alright, start up MAT Pose Edit and load up either CR2 for Sara, or the MAT pose for the texture you are editing, in my case I am opening the MAT pose for Galina.
Holding CRTL, scroll through the list of Sara's material zones, clicking and selecting all the parts of Sara's head. Your parts may differ from the ones shown in the screen capture if you are using Sara 2, but I'm sure you can tell which ones are for the head.
Now click Invert Sel from the buttons just right of the parts list. Everything but the Head material zones should now be selected.
Click Delete from the buttons left of the parts list, now only Head zones are left.
Click the Lips zone from the list and click Invert Sel, everything but the lips are now selected.
Reassign all of the Head parts EXCEPT the lips to the new texture you've created WITHOUT lips.
Click Invert Sel again and now only the Lips are selected.
Reassign the Lips zone with the new texture you have created with ONLY lips.
Save As… a new file, make sure not to save over the original MAT pose unless you are sure you will not need it again.
Now we have separate textures for the Head and the Lips and when you apply the MAT pose to either Sara1 or Sara2 it will only apply the lip texture to the Lip material zone, thus making a nice smooth edge all around the lips.
You might encounter some problems if the original creator of the texture did not make the lips larger then the Lip material zone. If you are creating your own textures I would recommend making the lip texture a smidge bigger then needed just to make sure you are getting full lip coverage on both models. All excess will be cropped of if it doesn't fit in the Lip zone.
This method also helps if you want to make a high resolution material for Sara's lips without having to make the entire Head texture hi-res.
If you are planning on releasing a texture set created like this there is no need to include the original base texture where the lips are applied to the head, it will just add to the file size.
Since the Galina texture was created for Sara1 there's not as much of a difference, but it does clean up the top lip a bit.
I hope this tutorial has been of help, please contact me with any questions: firstname.lastname@example.org