It's really easy. With Photobucket, just go and make an account. When you find a Photo on the web you like, right-click and save it's location.
Go to your Photobucket account and click Upload. It gives you a ton of options, but you need to click "The Web" option. Right-Click the space they give you and Paste the URL of the Photo you saved earlier. Click "Start Upload". When it is done, it gives you a new URL for your Photo. Right-Click save that and paste it in "Insert Image" and your done.
If you don't want to creat a PB account, then just use Imageshack. Right-Click and save the location of a Photo you want to post. Go to imageshack.com. Where it says "Upload", click the "url" option. Paste the URL of the photo you saved earlier and hit "Upload Now". Right-Click save the new URL they give you and use it in "Insert Image".
Both ways only take a minute to do.