What you've just done is to assign the block to the server. That is, to configure our routers so those IPs are routed to your server.
That's done and it's alrigth. Now, you have to configure those IPs in your server. That is, if you want to use those IPs for hosting, you can configure them through Plesk or manually (
http://help.ovh.com/ipalias).
If you want to use the IPs for Virtualization on Bridge mode , follow this guide:
http://help.ovh.com/BridgeClient