Hi
You can use an Excel document as a mail-merge source document. However you seem to be indicating that you want to use particular cells in Excel as your source data. If this is the case and it will always be the same cells you could paste a link in your Word document to those cells. For example right click in your first cell in your worksheet and select copy, then move to your Word document and right click at the position you want to paste and select Paste Special followed by Paste Link.
Hope this helps.
Tony