I don't think you can on ESXi, unless you are in unsupported mode. I have done it on ESX a few times, but the recommended way to backup the files from esxi are over the network, using the vSphere client. If at all possible go that route, it's much easier.
With that said. Format the disk with ext3 (You only have read support for NTFS, and FAT32 is not good with large files). Plug in the drive.
tail /var/log/dmesg Should tell you the name of the drive. Create a mount point and mount it, specifying the correct fs
mkdir /mnt/usb mount /dev/<device_name> /mnt/usb -t ext3 You will probably have to use vmkstools to export the files.
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