The software will probably be the most expensive part.Ability - M$ Works - Open Office - M$ Money - Intuit - Sage et alia.
A local lad should be able to make a PC for you, for about £300+ vat. The most expensive part of which will be XP.
You do not need a separate sound card or graphics card but you do need a minimum of 256Mb RAM, floppy drive and a CD-RW. Maybe a modem.
The rest is window-dressing.