for this image, the lasso tool is probably not the best selection tool to use.
I recommend creating a nice smooth 'path' using the 'Pen Tool'. You can then convert the path you make to a selection and use this to create a layer mask, that will hide your background.
This is 'non-destructive' method of editing. Meaning, that you have not erased (destroyed) any pixel data, simply hidden it via the use of a layer mask. The advantage? Well it means that you can edit your path, and/or mask in the future if you ever need too. One of PS's strengths.
If you have not used the Pen Tool before, you might find it a little hard to get used too, but I seriously recommend spending the time. You wont believe how useful (essential) this tool is!!!
Ok, check the tuts here at PSG for a pen tool tut (Marks gonna slap me for not knowing immediately! my bad), or check out the pen tool tut at
www.gurusnetwork.com
The Pen tool for this image would be the best method imho...
good lluck and lets us know how you do!