"ANYRD PayPal Cart Component" server script advice

http://anyrd.anyrd.com/home.html#ppcc
Im thinking of buying this component so i can sell tshirts from my website.
The only thing is that each of my tshirts are 1 offs so when the buyer completes a paypal transaction i want that tshirt to be ‘closed’ so that no-one else can come along and buy it again before i get a chance to update the site.

I emailed this question to their admin and they said “This is certainly possible, but it would require some custom actionscripting as well as a server side script to keep track of the stock. The component can not handle that type of thing automatically”.

which is great but i dont really know where to start scripting something like that. (What actually is server side script?! Im trying to avoid getting into databases and all that which i dont have a clue about. Im a bit of a newbie who has managed to bolt my site together over the last year or so by picking up bits of actionscript here and there so I do need it spelling out a bit!
Basically how difficult would it be to develop a system where completion of a Paypal payment updates a stock check which then says ‘sold out’ on my flash site. It sounds complicated just explaining it.
Thanks a lot, apologies if this is in the wrong forum.
Nick
http://www.mooschool.co.uk