I haven't actually flashed an Xecuter 1 before, but this should help you.
To flash the chip, you need to find the bios you want and a 100 MB dummy file. Make the bios file the right size for your chip (using some bios tools). Burn them to CDRW in Nero (data mode, slow speed.) Then insert your disc (with chip to bank 1, write unprotected), and the chip should automatically flash.
Use the search button, and the tutorials on XS for an exact guide: http://www.xbox-scene.com/tutorials.php
If it worked well, you should now be able to boot up your evox CD.
Xbox games can vary from as small as a few hundred megabytes (Galleon) to several gigs (The Matix.) Usually, they average between 2.5-4.5 gigs. A stock HDD can usually fit an absolute maximum of 4 games.