2) Also, is there a way two have the 400 columns split into 2 lots of 200
column data sources and import both together?
Not using mailmerge. You may be able to get the data out using ADO, but it
may not be able to "see" anything beyond column 255/256, even named ranges
that start at column 201 and end at column 400. I haven't tried this. If you
can get ADO to work you would probably be better off "rolling your own"
merge, e.g. using DOCVARIABLE fields to insert the data.
3) Futhermore, does microsoft access also have the 256 column limitation?
Yes (probably 255 or possibly even 127). As far as I know, all Microsoft's
"desktop database drivers" (which are mostly Jet drivers/providers or its
successor, ACE) and providers have a 255 maximum - even SQL Server.
1) Is there any chance that microsoft will extend this in the short term
future?
We are volunteers and do not work for Microsoft, so all I can say is that I
reported this specific problem some time ago and it was described as a
"Product Limitation". I do not know what that means in terms of future
fixes. I have also tried to point out that it is becoming increasingly
difficult to work with any kind of data source beyond this limit. However,
the focus in 2007 was clearly on the user interface, the XML file formats,
and as far as working with "data sources" is concerned, on Content
controls - I suspect the "approved" way to do this kind of thing would now
consist of a bunch of .NET code to transform your Excel worksheet's data,
stuff it into the appropriate data portion of a WOrd XML file, open the WOrd
document and let Word fill the content controls from that XML data. But
there's nothing in that lot for the non-technical Word user.