Md5sum and sha1sum values are provided in the download page.
Did you copy the ISO into USB and booting from USB, what method you followed to get ISO files into USB and make it bootable.
Or
Are you having ESXi5.1 in USB and trying to upgrade to 5.5. In this case, did you burn DVD/CD using ESXi 5.5 images. Can you please post the screenshot.
You can customize the ESXi5.5 image using the driver provided in https://my.vmware.com/web/vmware/details?productId=353&downloadGroup=DT-ESXI55-LSI-MEGARAID_SAS-660060001VMW.
This driver is support following controllers
The LSI MegaRAID driver supports products based on the 2008, 2108, 2208, 3004, 3008, and 3108 ROC families in various port counts. 2008 based Model 9240. 2108 based Models 9260 – 9264 and 9280 – 9284 including cv/cc models. 2208 based Models 9265 – 927x and 9285 – 928x including cv/cc models and Nytro models 8110 and 8120. 3004 based Model 9341-4i. 3008 based Models 9340-8i and 9341-8i. 3108 based Models 9361-4i/8i, 9380-4i4e/8e, 9360-4i/8i/24i8e. - See more at: https://my.vmware.com/web/vmware/details?productId=353&downloadGroup=DT-ESXI55-LSI-MEGARAID_SAS-660060001VMW#sthash.lTeRSTab.dpuf