I don't think Access comes with much in the way of drawing functionality even in VBA (there's a circle drawing tools for reports but thats about it). Nevertheless, one solution is to create a picture of a circle (with a transparent background) and then use VBA to change its size.
This isn't so straightforward because Access doesn't seem happy to show transparent backgrounds as transparent. However, Stephen Lebans (who just seems to love this kind of stuff) has a solution
here. Take a look around Stephen's site as it might give you some other options/ideas.
I gave it a try and it worked. Once you have the image on the form you can of course manipulate it like you would any other object i.e. change the width/height/position etc. I did this using buttons to change the image size. Not sure how you would use the mouse to do this but I've seen loads of postings about using the mouse so maybe they will help. If you are thinking of using the handles of the object to size as you would in design mode then I really don't know how you would easily do this. I guess you could use the OnCick event to select the circle which has some code to allow you to use the cursor keys to move the image and a similar sort of thing for resizing (although I'm not very familiar with how you'd go about doing this in VBA).
Somehow though I feel this isn't really what you want since all you are doing here is literally putting a circle on a form. It doesn't get saved in any record. However, there's no reason why you can't save the settings of the circle for each record so that when your next record comes up, the circle will set itself to the right place on the image for that record.
Just one other thing, if you try this then you might want to check out the settings of Size Mode in the object as it affects the way the circle would be stretched. The setting of Stretch seemed the logical option.
hth
Chris