Problem with the Keyword Tool

I am trying to figure out what’s a good amount to spend on a new google adwords campaign but I am having some difficulty doing this because the figures I am getting from the Google Adwords keyword tool just don’t make any sense. The numbers I get for global monthly searches and estimated impressions is far less than the figures I’ve seen in actual impressions for an active adwords campaign that I am currently running for some of the same keywords.

I’m talking about a difference of 6,255 actual impressions vs. an estimated 16 impressions for one keyword.

Can anyone explain how and why this is?

I don’t know much about Adwords, but could it be that you’re not bidding enough to be seen on the first page? Also, the 6,255 searches are global - are you targeting a particular region that would bring in leass searches than global?