Last week for Windows XP with Service Pack 1
As previously announced, Microsoft will stop providing support for Windows XP with Service Pack 1 and 1a from 10 October. After this date, patches and updates will only be released for Windows XP with Service Pack 2. The installation of SP2 is highly recommended anyway, since Windows XP is significantly less secure without it.
SP2 can be acquired via Windows Update (using IE only via this link), as direct download or on a free CD (subject to availability) from branches of PC World. An overview of MS product support time frames is available at the Microsoft website.