|You can wipe it completely, using one or two utilities available.|
You can certainly remove all your files etc., and empty recycle bin and defrag it.
You can reformat it using any current OS.
If there is no recovery partition (did you check the various options in the manual?), then you can legally use a compatible windows disk to re-install windows, using the keynwhich will be found on a sticker on the laptop. You can also download an ISO for your OS, burn to a DVD and use that DVD to re-install. You will need an OEM disk however you get one.
Not sure if you can secure/obtain a recovery disk from Asus; have you checked that possibility?