Hi there,
I had the same error about install.wim aswell, even after several reboots. What I did to fix it:
1. Copy the
drivers for your motherboard's SATA-controller to a diskette or USB stick (I used the Vista 64-bit version of mine).
2. Boot from your Windows 7 DVD and at the screen that says "Install now" select "repair....".
3. Press Load
Drivers and browse to your SATA-controller
driver. Select and press "Add
drivers" (no need to select anything in the list).
4. After drivers are loaded, just close the repair window, and press the "Install now" button.
5. Installation should work now!
The above names and buttons can be different from the installation disc, can't remember them all exactly. This worked for me and didn't need to reburn or put the installation files on an external harddisk

Seems Windows loads the appropiate drivers for your SATA controller, after which it can read the install.wim file correctly.
Used Windows 7 x64 version burned to Verbatim DVD+R.
Hardware in use:
- Asrock 4Core1333-FullHD motherboard with ATI™ SB600 southbridge
- Intel E2200
- 6 gb of RAM
- Samsung DVD-/+/RAM SH-S203D
I haven't found this solution anywhere on the internet yet. Hope this can help some of you!