Fix picitures in a wordpress site

I am working on a website ( so not yet live ), and I'm having a few simple issues. But as I cannot program the php I need a little help. Firstly the pictures are causing me a big problem. When look at the menu you will see the thumbnails are all different sizes. As these picitures come from different sources I cannot get a standard size. So I would like wordpress to just resize them, no matter what size I upload it shows as a standard size. And in the item forsale page a standard size. I have tried to reduce the pixel size of the picitures, but they stay very large but with lower quality. Also you will notice that the longest picitures are being cut off at the top and bottom.
lastly but not such an issue. On the pahes the area at the right for adds etc, I would like to be able to put 250 x 300 height adds in there. But the space is less than 250 across. Have a look at the site at woowaternew.sh0p.co.uk and let me know if you can help.