There will definitely be an increased - and possibly increasing - risk by remaining on XP after official MS support ends. You should consider migrating to Windows 7 (or, of course, a non-MS platform) sooner rather than later.
Protection offered by Anti-virus and internet protection products, free or paid, will not offer cast-iron protection against new exploits developed to take advantage of the fact that (a) official XP support has ended and (b) considerable numbers of XP instances will remain in service for some considerable time yet.
If the vast majority of XP was likely to be replaced in short-order, hackers would be less likely to spend too much time writing exploits but given that evidence suggests there'll be a lot of users still dependent on XP well past April 2014, there is a large community for hackers to target.
Of course, it's a personal choice and where the hardware is a determining factor (older PCs not necessarily being suited to or capable of running a newer OS) many will be faced with replacing both PC and OS. They may find the potential cost a problem but there are plenty of outlets available for reconditioned PCs or workstations with contemporary OS e.g. Windows 7 at very reasonable rates.
My recommendation is - upgrade. You really don't want to have your network and data compromised. It might not happen, but if it does...
