Properly size table elements

(See attached screenshots for clarity) .

When opening USB-Creator, the CD-Drive/Image and Disk to Use table elements are not properly sized to show they are empty.

And then when adding a disk or ISO image, the table elements resize, but not enough and user is given a scroll bar for a single element in the table (not a great visual layout).

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: usb-creator-gtk 0.2.30 [modified: usr/share/doc/usb-creator-gtk/changelog.gz]
ProcVersionSignature: Ubuntu 3.0-3.4-generic-pae 3.0.0-rc5
Uname: Linux 3.0-3-generic-pae i686
Architecture: i386
Date: Sun Jul 10 09:07:16 2011
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_AU:en
 LC_CTYPE=en_US.UTF-8
 PATH=(custom, user)
 LANG=en_AU.UTF-8
 SHELL=/bin/bash
SourcePackage: usb-creator
UpgradeStatus: Upgraded to oneiric on 2011-06-14 (25 days ago)