The march toward Windows XP's retail and OEM June 30 retirement party continues. Four weeks from today is Microsoft's deadline for mainstream computer makers to stop selling new PCs with the old OS, and the date the Redmond Wash.-based developer will stop shipping boxed copies to retailers.

Mark it as T minus four weeks and counting.

We follow up on last week's inaugural FAQ with more questions and answers, including clarifications on inventory and news of one online retailer dropping XP's price by more than 10 percent.

Must retailers stop selling XP after midnight of June 30?

No, says Microsoft. Although it's calling June 30 the retail and OEM availability end-date, the demarcation between selling and not-selling won't be razor sharp, the company said last week.

"The exact cut-off day for selling Windows XP is determined by OEMs and retailers, who can keep selling standalone versions as well as PCs with Windows XP preloaded by OEMs distributed prior to June 30, 2008, as long as their supplies last [emphasis in original]," a Microsoft spokeswoman said last week in an e-mail.

In other words, unless a retailer has pared its XP inventory to the bone, expect to see copies still selling into July, perhaps longer. Likewise for already-built machines that have XP installed, since dealers won't be required to yank them off shelves on July 1, but can clear their inventories at their own pace.

If system builders can continue to sell PCs pre-loaded with XP until Jan. 31, 2009, does that mean I'll be able to buy the OEM edition of Windows XP at retail or online until then?

No. And we can see the confused look on your face from here.

The retail version of XP Home or XP Professional dubbed "OEM" is also often called the "system builder" edition, in that it uses the same EULA (end user licensing agreement) as the OEM licenses that large computer makers and smaller shops install on the PCs they build and sell.

Retail OEM versions of Windows XP are considerably cheaper than either upgrade or full license versions of the same version; Windows XP Home in OEM costs just US$79.99 on Newegg.com, for example, while the upgrade version runs $99.99 and the full license is priced at US$191.49.

OEM versions are cheaper because they don't include free tech support from Microsoft, and legally you're not allowed to transfer the OS from one PC to another, say from an old, creaky piece of junk to something more up-to-date.

But even though "system builders" -- companies or individuals who have registered as a Microsoft Partner and then acquire Windows licenses through one of Microsoft's authorized distributors -- can get their hands on XP through Jan. 31, 2009, you won't be able to get the exact same license via retail once sellers exhaust their supplies after June 30.

"The June 30, 2008 deadline applies to OEMs and retailers for all versions of Windows XP," a Microsoft spokeswoman confirmed last week when asked for clarification.

Clear?

Yeah, we thought so, too.

Have XP retail sales increased as the June 30 deadline approaches?

Not really, says the NPD Group, a market research firm that specializes in tracking retail sales.

"Sales of XP have been pretty stable all year," said Michael Redmond, an analyst with NPD. According to the company's data -- acquired primarily from brick-and-mortar retail stores, but also from the likes of Amazon.com -- XP's retail sales are about 50 percent of what they were pre-Windows Vista. But with the exception of a dip last fall, which Redmond attributed to the launch of Apple's Mac OS X 10.5, aka Leopard, XP sales haven't changed appreciably since early 2007.

Will Microsoft's support for Windows XP also dry up June 30?

No. Although the company is putting XP to rest, availability-wise, it's sticking to its support commitments. XP's "mainstream" support, which includes non-security fixes and free phone support for retail copies, doesn't end until April 14, 2009.

Additionally, Microsoft will provide free security patches for XP -- the primary part of what it calls "extended" support -- through April 8, 2014.

Has there been any change in XP's retail price since last week?

Yes. Of the three online technology outlets -- Amazon.com, Buy.com and Newegg.com -- we started tracking last week, one dropped its price 11 percent. Last week, Newegg.com priced Windows XP Home OEM -- the least-expensive version of the operating system, but also the one that comes with the most restrictions -- at US$89.99, shipping included. During the three days before Monday, June 2, Newegg.com listed the same SKU at $79.99.

The other two online retailers we're tracking -- Amazon.com and Buy.com -- didn't budge on price.

On eBay, however, the average lowest "Buy It Now" price, shipping included, for a legitimate copy of Windows XP Home OEM was 1.1 percent higher this week than last.