For nearly a year, television and Internet audiences have been seeing a familiar string of ads from Apple attacking rival Windows-based computers. With this week's release of Windows Vista, the newest jabs aren't any friendlier.

In one ad, the character personifying the PC is dressed in hospital patient garb, talking about how he's set to undergo major surgery to upgrade to Vista. He then saunters off, telling the Mac character that if he doesn't come back, Mac can have his peripherals.

In another ad, a man pretending to be the Mac character heaps praises for the PC — until the real Mac character steps in, confounded, asking ''What's going on?'' The fake Mac replies, ''Nothing,'' and then mutters ''I'm a fan'' as he walks away.

On its own Web site, Apple Inc. tells visitors to get a Mac, stating, ''Why upgrade to Vista when you an upgrade past it?''

Microsoft Corp. launched Vista on Tuesday, its first major overhaul to the Windows operating system in five years. It features sleek new graphics, better search capabilities, improved security measures and multimedia tools, as well as more advanced parental controls and gaming support.

Yet Microsoft detractors, Mac users, and even PC-oriented magazine editors are pointing to how some of those features already exist on Macs. And Apple — set to release its own upgrade to its Mac OS X operating system, code-named ''Leopard,'' this spring — has already promised more innovations, such as automatic backups of files and advanced animation features.

The Cupertino-based company has repeatedly ribbed Microsoft to ''start its photocopiers.''

Representatives of the Redmond, Wash.-based rival declined to comment Wednesday, following its typical stance of not responding to Apple's marketing ploys.

The series of ''I'm a Mac — I'm a PC'' advertisements debuted last spring and are an extension of Apple's broader campaign to attract Windows users to the Mac platform. Windows remains the predominant platform for personal computers, though Apple's share of the PC market in the United States grew to 4.7 percent in the October-December quarter, up from 3.6 percent a year ago, according to technology research group IDC.

It's unclear if the ads have had a direct effect on Mac sales, but analysts say they have played a role in raising the public's awareness of Apple, alongside the immense popularity of the iPod player, Apple's growing number of retail stores and its new line of computers using Intel Corp. chips.

The ads have been criticized by some as too derisive, but many pundits, including bloggers who say they are Windows users, admit that the commercials are entertaining.

The video commercials star actor Justin Long personifying a Macintosh, and author and comedian John Hodgman personifying a PC. The Mac character is always portrayed as hip, cool and confident. The PC character, pudgier and older, is frequently portrayed as staid, dorky and a bit clumsy with its failed attempts to one-up the Mac in some way.

The underlying themes tout the Mac as more secure against virus attacks or more slick, with easy-to-use software to make movies or slideshows. The PC is usually trumpeted as a great but boring productivity tool that can't handle creative assignments very well.

About two dozen of the commercials have aired, spawning a smattering of goofy amateur spoofs as well.