How to configure OWA 2003 Attachment Blocking?

How can I configure Internet Security and Acceleration Server to publish OWA on an Internal Exchange Server?

The ISA Server allows for traditional mail server protocols (SMTP, POP3, IMAP4, and so on) to be published easily under the Server Publishing Rules node. However, no ISA Server wizard automates publishing an internal mail server that allows mail retrieval by using the Hypertext Transfer Protocol (HTTP). 
This article assumes that the following prerequisites are in effect:

MS KB 555001 by William Lefkovics (MS Exchange MVP) has more info:

There are 2 levels of file attachments for Outlook Web Access. Level1 attachments have file extensions that are prohibited from accessing by OWA. Level2 attachments have file extensions that can be accessed, but only if saved to the client's file system first.
OWA is installed with a default set of file extensions for the two levels as shown in the following registry keys:

Level 1 attachments

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeWeb\OWA

Value: Level1FileTypes
Type: REG_SZ
Value Data:

ade,adp,app,asx,bas,bat,chm,cmd,com,cpl,crt,csh,exe,fxp,hlp,hta,inf,ins,isp,js,jse,ksh,lnk,mda,mdb,mde,mdt,mdw,mdz,msc,msi,msp,mst,ops,pcd,pif,prf,prg,reg,scf,scr,sct,shb,shs,url,vb,vbe,vbs,wsc,wsf,wsh

Level 2 attachments

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeWeb\OWA

Value: Level2FileTypes
Type: REG_SZ
Value Data:

ade,adp,asx,bas,bat,chm,cmd,com,cpl,crt,exe,hlp,hta,htm,html,htc,inf,ins,isp,js,jse,lnk,mda,mdb,mde,mdz,mht,mhtml,msc,msi,msp,mst,pcd,pif,prf,reg,scf,scr,sct,shb,shs,shtm,shtml,stm,url,vb,vbe,vbs,wsc,wsf,wsh,xml,dir,dcr,plg,spl,swf

Attachments listed should be separated by a comma with no space.