Should be easy enough and cost no more than R1000
Something like :-
Wireless Lan Router :-
http://www.sybaritic.co.za/store/product_info.php?cPath=100_122&products_id=1225
And a PCMCIA Wireless LAN card :-
http://www.sybaritic.co.za/store/product_info.php?cPath=100_122&products_id=1221
Of course, you can go slightly more expensive and opt for a 54mbs solution.
Here's the sybaritic networking page :-
http://www.sybaritic.co.za/store/index.php?cPath=100_122
As far as security goes, a wireless LAN Router like the one linked doesn't have a very strong signal, maximum 300M outdoor, 100M indoor, so your neighbours, if they knew what they were doing, could try to hook into your network and a war driver could hook into it from the street outside your house.
Most decent wireless LAN routers will have WPA (Wi-Fi Protected Access) built into the firmware, which offers a decent level of security.
http://sbc.webopedia.com/TERM/W/WPA.html
http://www.wi-fiplanet.com/tutorials/article.php/2148721
That will keep out all but the most determined - and those that are really determined would most likely need physical access to your equipment before being able to gain access to your network remotely.
Sentechs definition of Broadband - http://www.3r.co.za/bushboy/bb_sentech.gif