The error you are seeing means it is not liking the space in the path, and it is interpreting tha the path is only C:\Documents:
-javaagent:C:\Documents and Settings\PC\Bureau\JBossAOP\eclipse\jboss-aop-2.1.8.GA\lib\jboss-aop.jar-Djboss.aop.path=C:\Documents and Settings\PC\Mes documents\Downloads\travail\jboss\SINGLETONS\jboss-aop.xml
I would try adding " or ' to see if the problem is solved:
-javaagent:"C:\Documents and Settings\PC\Bureau\JBossAOP\eclipse\jboss-aop-2.1.8.GA\lib\jboss-aop.jar" -Djboss.aop.path="C:\Documents and Settings\PC\Mes documents\Downloads\travail\jboss\SINGLETONS\jboss-aop.xml"
or
-javaagent:'C:\Documents and Settings\PC\Bureau\JBossAOP\eclipse\jboss-aop-2.1.8.GA\lib\jboss-aop.jar' -Djboss.aop.path='C:\Documents and Settings\PC\Mes documents\Downloads\travail\jboss\SINGLETONS\jboss-aop.xml'
It's been ages since I stopped working on Windows, so I'm not sure which one of those would work. Another (lame) alternative is adding your stuff to a path that has no spaces in it.
You also need to add a space char before the -D, as I did above, otherwise it won't work.