That is pretty much what I did.  This was my response to them:

*Like I said, any client 6.4.0.1 and higher WILL NOT install on a W2K3 box!
 You are stuck/screwed. Your choices are:*
*
*
*1.  Upgrade the OS to 2008+*
*2.  Replace (uninstall/reinstall) client with highest supported client
(6.3.1.2) - requires complete/full/start-all-over-again backup (delete
existing backups) since you can't downlevel the client*
*3.  Live with it!*
*
*
However, unless I missed something, I don't think the APAR blocks install
on W2K3 until 6.4.1.  On this page (
http://www-01.ibm.com/support/docview.wss?uid=swg21608346),  IC89603 is
listed under "*Interim fix 6.4.0.1 - Available January 31, 2013*" yet I
have two installed 6.4.0.11 clients on W2K3 servers/systems.


On Mon, Sep 16, 2013 at 1:41 PM, Schaub, Steve <Steve_Schaub AT bcbst DOT 
com>wrote:

> Easy - tell the Windows Engineers to upgrade the O/S to W2K8-R2 on all the
> servers they installed TSM 6.4 on!
>
> -----Original Message-----
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf 
> Of
> Zoltan Forray
> Sent: Monday, September 16, 2013 11:57 AM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Re: [ADSM-L] Windows Clients and Non-Supported OS Levels
>
> Well, now I have the user/administrator asking if they can/should upgrade
> the 6.4.0.0 client (and how-high)?  Can't really back down since this
> server has 21TB / 26M objects in backup.  It would require starting all
> over from scratch.
>
> Of course, since 6.4.0.1 now detects the OS level and prevents it from
> being installed on W2K3 boxes, I am guessing they are stuck!
>
>
> On Mon, Sep 16, 2013 at 11:23 AM, Prather, Wanda <Wanda.Prather AT icfi DOT 
> com
> >wrote:
>
> > I agree it shouldn't be that way.
> > Anybody ever put in an RFE for that?
> >
> >
> > -----Original Message-----
> > From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf
> > Of Zoltan Forray
> > Sent: Monday, September 16, 2013 9:34 AM
> > To: ADSM-L AT VM.MARIST DOT EDU
> > Subject: [ADSM-L] Windows Clients and Non-Supported OS Levels
> >
> > This is mostly a gripe at IBM..........
> >
> > Why do the Windows clients allow themselves to be installed on
> > non-supported OS/levels? or at least issue warnings?
> >
> > My Windows folks (yes, they are being lazy and not reading all the
> > readme/docs), are constantly installing miss-matched/not supported
> > clients (i.e. 6.4 on W2K3 servers, which is not supported per
> > http://www-01.ibm.com/support/docview.wss?uid=swg21197133).  Then of
> > course, they can not be  downleveled.
> >
> > When someone contacts me about issues with their client/backups and I
> > say "not supported combination of OS and TSM client level", their
> response is, "
> > *then why did it let me install it if it isn't supported on this OS*"
> >
> > --
> > *Zoltan Forray*
> > TSM Software & Hardware Administrator
> > Virginia Commonwealth University
> > UCC/Office of Technology Services
> > zforray AT vcu DOT edu - 804-828-4807
> > Don't be a phishing victim - VCU and other reputable organizations
> > will never use email to request that you reply with your password,
> > social security number or confidential personal information. For more
> > details visit http://infosecurity.vcu.edu/phishing.html
> >
>
>
>
> --
> *Zoltan Forray*
> TSM Software & Hardware Administrator
> Virginia Commonwealth University
> UCC/Office of Technology Services
> zforray AT vcu DOT edu - 804-828-4807
> Don't be a phishing victim - VCU and other reputable organizations will
> never use email to request that you reply with your password, social
> security number or confidential personal information. For more details
> visit http://infosecurity.vcu.edu/phishing.html
> -----------------------------------------------------
> Please see the following link for the BlueCross BlueShield of Tennessee
> E-mail disclaimer:  http://www.bcbst.com/email_disclaimer.shtm
>



--
*Zoltan Forray*
TSM Software & Hardware Administrator
Virginia Commonwealth University
UCC/Office of Technology Services
zforray AT vcu DOT edu - 804-828-4807
Don't be a phishing victim - VCU and other reputable organizations will
never use email to request that you reply with your password, social
security number or confidential personal information. For more details
visit http://infosecurity.vcu.edu/phishing.html