You can follow these steps to accomplish that in Windows Vista:
1.) First, right click on your desktop and select Properties.
2.) Inside that window, choose the option of Appearance and then click Advanced.
3.) From the options above, select Item and then under the pull down menu, select Icon Spacing (Vertical). You can then choose the size you’d like your icons to be. Similarly, you can perform the same thing for Icon Spacing (Horizontal).
4.) Click Apply and then OK.
5.) Next, right click on your desktop and choose Arrange Icons By. Then select the option of Align to Grid.
6.) You can then repeat step 5 again if necessary, in order to make the changes you want.
That’s all you have to do to start enjoying your brand new icons!
~ Ramachandran Kumaraswami