Adding sort/shuffle function to admin & front page to a shop

HI guys, I have a web site that needs a sort/shuffle feature added to it. My client wants to be able to pick a category, (or a product if in the product area), and then change its sort number to whatever they like, say from number 9 spot to the 3rd spot, click the update button and it changes that category or product to that number they chose and at the same time it also shuffles the rest of the numbers so they all show up from 1,2,3,4,5,6 etc-whatever. The way the site is set up at the moment is the client needs to click the product or category listing up one spot then the page refreshes then click up again and it goes up or down one spot, then do this again and again to shift the one product or category up spots, as you can see it can take 30 clicks to shift one thing up 30 spots and its not time efficient for the client and waists time. I need someone who knows what they are doing to do this within a few days if possible. If you have different idea on what can be done to change things then I am open to ideas. One things tho, the site must not go down or be changed in anyway from what client sees now, so what I mean is you will need to copy the site or page/pages and put them somewhere else so that when the work is done and myself and the client are happy the changes can be uploaded to go live but only after approval as client is fussy. Cheers Jamie