Bio-Balance's simple solution to search a sequence based on GI Numbers using NCBI Website:

Go to : http://www.ncbi.nih.gov/

Search : Protein and enter the GI Number for which you want the sequence in the space provided and click GO:

Example key in the # as:1001516

Click on BAA10143 in the new redirected page.

You get the sequence for the GI number you entered in the lower half of the new page.