First of all, your Blog should have a program which allows you to install a banner. If this the case, there are instructions how to do it, you have simply to read and follow what is recomended.
Simply select one of SFI or TripleClicks Gateway banner, open it, then copy please not the Picture/Photo rather, copy the HTML Code and then paste it into your Blog or own web. After doing this, publish it, that is all.
