RODBCType&NullDataExportProblems

Hello
I am trying to move data between R and other systems (e.g. SAS and MS
SQL Server) using RODBC.  I think I have the most recent version of
RODBC (0.9) and here is some other system info:

odbcGetInfo(channel)

[1] "Microsoft SQL Server version 08.00.0679. Driver ODBC version 03.52"

version

         _
platform i386-pc-mingw32
arch     i386
os       mingw32
system   i386, mingw32
status
major    1
minor    6.1
year     2002
month    11
day      01
language R

I appear to be having 2 sets of problems when I execute an sqlSave to
export an R dataframe to either SAS or to MS SQL:
1) RODBC seems to deal with chars and int types OK -- but seems to want
to create "double" types in the receiving systems which don't support
"double"s (instead -- for example -- MS SQL supports "float").  How can
I specify more precisely the data types to be created in the receiving
system?  If this is documented on the R site, or in the RODBC docs, I
have missed it.

2) So if I create a file with chars and ints in MS SQL it seems to work
OK -- until I have missing data in the data frame (e.g. int NAs).  I
have not yet hit upon the way to write nulls to the receiving system.  I
have played with "nastring=" and each time I get:
"[RODBC]Failed exec in Update22005 0 [Microsoft][ODBC SQL Server
Driver]Invalid character value for cast specification "

In my defence, I have spent many hours trying to sort these issues out.
What am I missing? Any help would be much appreciated.