Sorry I didn't realize 2.1.0.Final did not contain the 3.2 modules, another thing to be fixed :) . Could try with this: http://downloads.jboss.org/snowdrop/2.0.5.Final/jboss-spring-subsystem-as7-2.0.5.Final.zip, I checked it does contain the spring 3.2 modules. As far as I know snowdrop should not require a class from spring-tx, but if for some reason your project makes it reference something from it then you could download it (http://search.maven.org/remotecontent?filepath=org/springframework/spring-tx/3.2.3.RELEASE/spring-tx-3.2.3.RELEASE.jar) and put it in $JBOSS_HOME/modules/org/springframework/spring/snowdrop. Finally add <resource-root path="spring-tx.jar" /> to module.xml.
Hopefully that will get you past that error.
Cheers,
Tejas M.