When Microsoft releases its second service pack (SP2) for the Windows XP operating system, expected in June, there will be extra features for Tablet PCs. These additions promise an improved user interface and additional tools for developers, but will there be enough to popularise this type of pen-based computer?

The Tablet PC has been on the shelves for 18 months but take-up has hardly met the stellar success hoped for by Microsoft and its hardware partners.

The razzmatazz and hyperbole of the launch failed to impress IT industry analysts at Gartner and IDC. Both estimated sales of around 425,000 units in the first year, and these predictions have proved disappointingly accurate.

The slow take-off has angered hardware manufacturers that invested in the format, and some have blamed Microsoft for not doing enough to encourage sales of the new product.

Acer is a staunch supporter of the Tablet PC and was been using the format for Microsoft on a trial basis for more than two years ago. Last year, Acer's president, Mr Wang Chen-tang, blamed disappointing sales on the costs levied by Microsoft for the Windows XP Tablet PC Edition operating system.

In October, Mr Adrian von Hammerstein, Fujitsu Siemens's president and chief executive, said that sales of Tablet PCs had not altered sales in the company's pen-based computing markets, and were disappointing in horizontal markets because of the lack of applications.

He felt that Microsoft should encourage independent software vendors to develop general applications that apply to all industry sectors.

Microsoft is responding to the criticism. Last month it launched a contest for developers, entitled "Does Your Application Think in Ink?" Entries will have to demonstrate innovative uses of the Tablet environment. The winner of the $100,000 (€83,830) prize will be announced in September.

For hardware vendors, Microsoft has developed extra features, code-named Lonestar, for Windows XP SP2.

This includes a new Tablet Input Panel, which displays the on-screen keyboard and text input panel. It converts handwriting on the fly to make correcting text before entry easier.

It can also be linked with the input fields of an application so that only certain words, characters or digits are recognised. This is supported in the new software development kit.

But will this bring out the "corridor warriors" - the mobile executives hailed as a principal target?

Mr Brian Gammage, a vice-principal at Gartner Research, does not believe that Microsoft's actions go far enough.

He thinks the system is immature and needs to recognise gestures - standard symbols for common functions such as delete, cut, copy and paste.

"Functionality is not integrated with the rest of the operating system," according to Mr Gammage. "These are major usability barriers that haven't been overcome."

Mr Gammage does not dismiss the Tablet concept. He is impressed with how intuitive the pen is as a pointing device and praises the Tablet as a sketching device.

However, he questions the premium paid to gain these advantages.

"Microsoft expects the original equipment manufacturers to handle cost, but they have little fat left to cut," he says.

Developing a Tablet PC is a serious financial commitment because of the need to develop extras, such as the special hinges for convertible laptops and making slate models light and rugged.

Acer's first machine cost £1,799 in 2002, but prices have now dipped below the £1,000 barrier. Other manufacturers have made similar cuts but the battle is to convince users that the pen technology offers a significant advantage.

If something is not done soon, the Tablet PC may eventually attract the sort of derision that killed Apple's pen-operated Newton.