When you want part of a document to have its own set of page number, different margins, different headers, different page orientation - basically anything to do with pages rather than paragraphs, you need to start thinking about section breaks. While Word has a setting of "Different first page", this is a fairly limited option.
First insert a section break at the end of your page one.
Go to the Page Layout tab, and select the drop down for "Breaks" and then select "Next page". [If you had a normal page break in, delete it, as it's not necessary if you're using the next page section break.]
Once you've got your section break, you're able to make changes to the parts of the document before and after the break.
Go into the header (or footer or wherever you've got your page numbering). To get there go to the Insert tab and select the Header drop-down and then "Edit Header" down the bottom of the list.
You will now see that you have a Header Section 1 and a Header Section 2. Make sure your cursor is sitting in Header Section 2 and then select the Page Number drop-down and select "Format Page Number".
In the Page Number Format window which pops up, change the selection from "Continue from previous section" to "Start At" and then type whatever number you want in the little box. Click Okay, and then exit your header.
My gods I hate Word 2007. I have to spend ages working out how to do things which were top of my head before this change.