the easiest way to do this is to do a freespace wipe. Any file deleted from the recycle bin isn't actually deleted, merely marked by Windows as deleted (the file attributes are changed, this means Windows sees the space the file occupies as free). eventually the space the deleted file occupies will be overwritten, but until then data can still be recoverable.
To do a freespace wipe, right click on the drive you want to perform the wipe on (eg C; Drive) in My Computer - the option is titled "Erase Unused Space" (note it is only the unused or free space you will be wiping, not the entire contents of the drive. Your data you want to keep will remain!
You will be asked if you are sure you want to erase unused space. before clicking "yes", you might want to change the default wiping option. The default is 35 passes (I think, I can't fully remember) - quite a lot and really quite unnecessary for most people (it will take several hours - it would take about 1.5 days on my computer). The safest options are either the 3 or 7 pass options - these will take a few hours at the most. the one pass Psuedorandom Data pass is even quicker (with this you can change the default number to any figure you wish). If you are using Eraser v.5.8 I think you also have quick option (first and last 2kb of sector(?)). If so, I advise you to use it with caution, and perhaps not at all - some people have found problems with their computer after choosing this option. I won't use this option. The other options have all been tried and tested by me and have all worked fine.
Make sure that in the options marked "Overwrite", the tick boxes for Free Disk Space and Directory Entries are ticked. You might want to tick the Cluster Tip Area option too, since old data can reside in the unused space of sectors that existing files occupy (complicated to explain! - briefly, sectors are fixed in size and a file will not use up all the space in sectors that it is written to, there is some "slack space"). Note that some files are "locked" by Windows (they are essential for the running of Windows eg drivers) and the slack space (cluster tips) of those files cannot be wiped.