Picture size problems

Hey, i am new pretty new to web design and am trying to create a picture gallery, i am trying to create thumbnails and am finding even though I have put for the sizes to be the same the photos in .gif are comeing out bigger than the ones in .jpg. I tried resiing them in photoshop but to find it also happened here.
Is there anything I can do about this?
Many Thanx
Rik

If it's the same pictures being different sizes then I don't know what to tell ya. Check the properties of the picture; most pictures have 72 pixels per inch, if they've got more, than well, to photoshop its only gonna recognize the pixels. What measurements are you putting in to try and resize it?

i was trying to resize them to have a width of 150,
at first tried to resize them just with using code, which was exactly the same for all of the pics, but the ones in .gif were comeing out bigger than all of the ones in .jpg.
So i tried resizeing them in photoshop, but again the .gif came out bigger
Dont know whats going on