(taken from officeusers.org)
In Word, click on the document where you want to insert the worksheet. Go to the Insert menu and select Object. Choose Create from File and click the Browse button. Navigate to the workbook with the worksheet you want to insert. Click on the file, click Insert and click OK.

In Word 2007 or 2010, click on the document where you want to insert the worksheet. Go to the Insert tab and click Object in the Text group. Go to the Create from File tab and click the Browse button. Navigate to the workbook with the worksheet you want to insert. Click on the file, click Insert and click OK.

You may notice when you are inserting the worksheet that you have a couple of options. Selecting Link to File inserts the contents of the worksheet into your document and creates a hyperlinked shortcut to the worksheet. If you make changes to the worksheet, they will be reflected in the document as well, as long as you still have access to the worksheet.

If you choose Display as Icon, Word inserts a nice little icon instead of the entire worksheet. Simply click on it to open the worksheet.

You can insert worksheets into other Office files, such as a PowerPoint slide or Publisher publication, in the same manner.

Remember, if you plan to move the file to another location, like another computer, all files must be moved including the linked Excel file. The best thing you can do is to create a folder and store all related files in the same folder, then move this folder.