Todays standard screen resolution is 1024x768 pixels. Some use higher res, some use lower, but this seems to be the most used res. When using a BB such as this with this screen res, the largest you want to upload a picture is 800pixels wide, as otherwise the screen is widened and you have to scroll along to see the pic, and also any text posts after it aswell - which is not fun!
So bear in mid when resizing your pics, not to go wider than 800 pixels wide!
Now, for you folk with graphics programmes such as Photoshop or Paint Shop Pro (personally I use PSP7) resizing is easy. Just open that programme, open the pic(s) you want to resize and go to your RESIZE option. With most of these programmes you can choose a percentage or a pixel...