XP was discontinued several years ago with the release of win7, XP is now loosing support. Your copy of XP will continue to work just fine... it will simply no longer get updates from Microsoft. Make sure you have a firewall (router), are using a decent antivirus, and are using an updated web browser (Firefox or Chrome) and you should be fine continuing with XP.
The other option is to hold out for win9 this fall or next spring as MS is fond of introducing a new OS with cheap entry prices (win8 was $40ea when I bought it). Granted, I am not sure that a PC designed for winXP is going to be modern enough or fast enough to run win9 when it becomes available.