Here is the answer from Bruce Hagen MVP OE
You no longer have spell checking capabilities in some languages in Outlook
Express 6.0 after you install the 2007 Microsoft Office system:
http://support.microsoft.com/kb/932974
Office 2007 breaks OE's spell check. Downloading a free spell check is the
simplest way around this.
Some free spell check programs.
Vampirefo:
http://www.majorgeeks.com/download.php?det=2952
TinySpell:
http://www.tinyspell.m6.net/ (Checks the spelling as you type).
Or from this blog:
http://pschmid.net/blog/2006/11/13/80
After installing Office 2007 RTM, you don't have English as a choice of
language in the spell checker of Outlook Express and potentially other
programs.
a.. Office 2007 is replacing the v.3 English Proofing Tools that shipped
in prior versions of Office with a new version (v.6). There are a number of
changes in this new version, but the one that is causing this problem is
that Outlook Express doesn't understand the new English Proofing Tools. This
is a problem because Outlook Express has never shipped with its own proofing
tools but has used the ones shipped by Office.
b.. There are a few scenarios in which you won't run into this problem:
a.. An upgrade from Office 2003 or earlier to Office 2007 RTM if you
don't manually uninstall the earlier version of Office.
b.. A configuration in which Office 2003 (or earlier) has not been
removed.
For example, I have Office 2003 still on both of my computers, and I
still have English in Outlook Express.
c.. The workaround for this problem is to install the English dictionary
from Office 2003 (or Office XP). There should be no need to install all of
Office just the dictionary. The English Proofing Tools can be found in the
Custom Install tree under Office Shared Features|Proofing Tools|English.
