Install another Office 2007 Proofing Tools (e.g. Dutch)
An update of this blog is available. In the new blog I explain how to use the Microsoft Office Multi-Language Pack 2007 and how to install extra Proofig Tools for Office 2007.
I'm working with Office 2007 now. Who isn't? Unfortunately Microsoft only released German, French and Chinese language packs. But proofing tools for other languages aren't available yet. When you have installed Office 2003 and you upgraded to Office 2007 Beta 2 you're proofing tools are automatically recognized and added to your new Office Product. Luckily you can install the Office 2003 tools afterwards as well. Just follow the steps and you're Office will be upgraded.
Step 1 Install Office 2003 (Custom Install)
Select only Proofing Tools and deselect all other options
Step 2 Install the additional Proofing Tools of your language
Select only your Language and deselect all other options

Update: Step 2b Deinstall Office 2003 (Tip of Suomi)
Go to Add/Remove programs and remove Office 2003 from the list
Step 3 Open a Office 2007 Product
This product will automatically integrate the Office 2003 Proofing Tools
Step 4 Select your Language options
Check your settings if the language is added
Step 5 Update your machine
This is the worst step, cause your brand new machine will have several Office 2003 updates, including SP2 and all kinds of updates for Word, Excel, e.t.c.
Update: Thanks to Suomi (step 2b), this will only update Proofing Tools, without any other updates for Office 2003 (e.g. the 110MB SP2)
Update: Step 6 Update OCR in documents (Tip of Ho)
Move the *.LNG files from /Program Files/Common Files/Microsoft Shared/MODI/11.0 to .../MODI/12.0.
Summary
Microsoft isn't able to deliver the correct Proofing Tools for Office right now. I hope they have solved this problem in the Office 2007 RTM. They don't have to deliver brand new proofing tools. If only they deliver the old ones but not recognized as a Office 2003 product.
Update:
Will there be an PTK for Office 2007
There will indeed be a Proofing Tools Kit (PTK), but it will not be marketed as it was in Office 2003. The 2007 PTK will actually be part of the Multi-Language Pack (MLP). This pack consists of 3 CDs. The first two CDs include all the Single Language Packs (SLP), each of which contain proofing tools (spell-checker, grammar checker, hyphenator, thesaurus…) as well as the localized user interface (UI) and localized Help for a given language. The third disc will contain all the proofing tools by themselves.
If a user just wants to add one or two proofing tools (say, they want to use a Russian or an Dutch speller, which is not part of the default English version of Office), they will be able to download the SLPs for those additional languages in which they are interested. But if someone is deploying many proofing tools languages and does not want the associated UI or are concerned about disc space, they will be able to purchase the boxed MLP and use the third disc. Enterprise customers that purchase the multilingual license will have access to any of these deployment methods.
This flexibility is designed to respond to demand from users. We have regularly seen on newsgroups that many individual users are interested in adding one or two languages to their own configuration. Being able to directly download and purchase a single set of linguistic tools (a speller, a thesaurus and a grammar checker, for instance) for a given additional language will meet many users’ needs.
What is the Microsoft Office Multi-Language Pack 2007?
The Microsoft Office Multi-Language Pack 2007 is an add-in product that can change the entire user experience of Office 2007 desktop applications by enabling each desktop to support many languages.. This includes Menus/User Interface, Help, Dictionary, Thesaurus, and Spell Checker. In addition to enhancing the user experience, a user can elect to use individual aspects of the pack, such as spell checker to proof a document in a language other than the default language set on their computer.
What languages are available?
The MLP will include tools for the following languages:
Arabic, Brazilian Portuguese, Bulgarian, Croatian, Czech, Danish, Dutch, English, Estonian, Finnish, French, German, Greek, Hebrew, Hindi, Hungarian, Italian, Japanese, Kazakh, Korean, Latvian, Lithuanian, Norwegian, Polish, Portuguese, Romanian, Russian, Serbian Latin, Simplified Chinese, Slovak, Slovenian, Spanish, Swedish, Thai, Traditional Chinese (HK), Traditional Chinese (Taiwan), Turkish, Ukrainian.
-- Thierry Fontenelle (Program Manager) & Jay Waltmunson (Program Manager) --