Use texView by BIS
(you probably know this for using to convert the other way around
) As you talked about Photoshop, I assume you have it: It's not possible to convert paa & pac to jpg...
How ever, int TexView, choose save type "AllFiles" and add the .tga extension after the file name....
This way you have a Tga file wich you can edit in Photoshop...
(you can't use paint to edit .tga images....