I've been looking for something similar myself, just got an R4 Card but a lot of the homebrew requires the RAM addon. So to be honest it's probably best to just buy a RAM addon then get the rom for the browser.
It's an expansion pack that was released with the Official Internet Browser to upgrade the systems RAM: Have what?
There's one on eBay.co.uk right now in buy it now from £10-15 there's like 4 of them listed. Just search "DS Memory Expansion"