I think you were thinking about last month's survey saying Apple has 14% of US retail PC shares.
http://www.appleinsider.com/article..._of_us_based_pc_retail_sales_in_february.html
I believe the retail market is only 20-30% of the total pc market (i.e. companies buy up 70-80% of the pc's sold).
The NPD data from that article you are referring to is better than this current data since it measures consumer retail computer sales only, but it still has many problems. First of all, it only covers certain brick and mortar retail stores.. it DOES NOT include sales from online websites like Dell.com or Apple.com. Secondly, it makes no attempt to breakdown sales into pricing segments.
I want to see Apple's market-share versus PC manufacturers in consumer-only computer sales divided into different pricing segments, since most of Apple's computer product line lies in the upper end of the market. It would also be interesting to see more detailed demographic statistics from that data, like Apple's market-share among "computer enthusiasts", percentage of sales are to "switchers", and longer term data about Apple's push into the education sector is creating long-term buyers out of highschool and College kids.