Thumbnails overlapping

Hello all,

I recently completed the adding thumbnails tutorial after modifying it to allow large images. Now, while i was doing that i used the normal thumbnails provided by this site. But after i put in my own their spacing has gone to hell. At first they are ok, but then they start to overlap and have giant gaps between them. I have no changed any code, merly the images in the .xml file.

I am thinking that it might be caused by the thumbnails being different sizes, but am unable to test this since i do not have the software here to resize them (only at school).

So my question to you guys is could this be the problem or is there something else which i can do now which will fix it? I used the tutorial mentioned below. It there any code or something which will fix the problem?

Thanks all

kirupa.com - Adding Thumbnails, Page 2