Neither PSE7 or PSE 8 have layer masks, apart from on adjustment layers. You can however download some useful plug-ins. I recommend Elements Plus or Grants Tools to my PSE students. Alternatively, you can 'hijack' a layer mask from a document created in Photoshop and merge it into the layer to create a layer mask. This method is a little clumsy but it works. You are however limited as you do not have 'apply layer mask' commands available.
Elements Plus also includes, curves, channels and a channel mixer in the Demo version for free. If you don't have plans to upgrade to Photoshop, I would definitely recommend adding the free plug-ins.