it sounds like you are inserting a picture of your bar code in the
worksheet. To get it to "lock" you need to insert a Picturebox control
and set the "Picture" property of the picturebox to the image file
that contains the bar code image.
To insert a picturebox control, select View - Toolbars - Control
Toolbox then find the Picturebox control in the toolbox and click on
it and finally draw a rectangle in your worksheet where you want the
picturebox. Next, right click on the picturebox in the worksheet and
select "Properties". In the Properties window find the Picture
property and set it to the image file name. Set any other properties
that you need for the picturebox and then close the properties window.
In the Control Toolbox, click the first icon to exit from "design
mode" and then close the toolbox.
If you use bar code fonts, you can restrict the bar code to the cell
however fonts are more difficult to use and they produce poor quality
bar codes. The best tool to use would be a bar code ActiveX control.
The best one on the market is from TAL Technologies at:
http://www.taltech.com/products/activex_barcodes.html