Sadly, you can't do that without VBA. There's no built-in function that you can use to find the active cell. The best I can come up with is to use a Selection Change event to store the row and column of the active cell in some unobtrusive location. Then you can use Conditional formatting to check that location. If that sounds viable, follow these steps:
1) Open the sheet you want to format.
2) Right click on the sheet tab on the bottom and select View Code
3) Paste the following code:
Rich (BB code):
Private Sub Worksheet_Selectionchange(ByVal target As Range)
[Y1] = ActiveCell.Row
[Z1] = ActiveCell.Column
End Sub
4) Change the cell references in red to where you want to put the activecell row and column.
5) Press Alt-Q to close the VBA editor.
6) Select the range you want to conditionally format. Let's assume the top left corner of the range is A1.
7) Click Conditional Formatting --> New Rule --> Use a formula
8) Enter this formula:
=(ROW(A1)=$Y$1)*(COLUMN(A1)=$Z$1)
where A1 is the top left corner of your range, and Y1 and Z1 are the cells you picked in step 4.
9) Click Format and choose a fill color.
10) Click OK and try it out.
Even this isn't perfect. It seems a little flaky, especially when you select a range instead of a cell.
Let me know how that works.