Yup. There's only one install DVD no matter what version you put on. That may be a big reason why Ultimate doesn't take up 100 GB. They had to trim it down so Home Premium purchasers wouldn't squawk.
-MilesAhead
Actually, there are a LOT of different DVDs for Windows 7. Here's an MSDN list with file sizes:
[font="Courier New"]
Windows 7 Enterprise N (x64) - DVD (English) 2,674 (MB)
Windows 7 Enterprise N (x86) - DVD (English) 2,030 (MB)
Windows 7 Home Premium N (x64) - DVD (English) 2,774 (MB)
Windows 7 Home Premium N (x86) - DVD (English) 2,125 (MB)
Windows 7 Professional N (x64) - DVD (English) 2,774 (MB)
Windows 7 Professional N (x86) - DVD (English) 2,125 (MB)
Windows 7 Starter N (x86) - DVD (English) 2,125 (MB)
Windows 7 Ultimate N (x64) - DVD (English) 2,774 (MB)
Windows 7 Ultimate N (x86) - DVD (English) 2,125 (MB)
Windows 7 Enterprise (x64) - DVD (English) 2,977 (MB)
Windows 7 Enterprise (x86) - DVD (English) 2,289 (MB)
Windows 7 Home Basic (x86) - DVD (English) 2,386 (MB)
Windows 7 Home Premium (x64) - DVD (English) 3,075 (MB)
Windows 7 Home Premium (x86) - DVD (English) 2,386 (MB)
Windows 7 Professional (x64) - DVD (English) 3,075 (MB)
Windows 7 Professional (x86) - DVD (English) 2,386 (MB)
Windows 7 Starter (x86) - DVD (English) 2,386 (MB)
Windows 7 Ultimate (x64) - DVD (English) 3,075 (MB)
Windows 7 Ultimate (x86) - DVD (English) 2,386 (MB)
Unique File Sizes:2,030 (MB)
2,125 (MB)
2,289 (MB)
2,386 (MB)
2,674 (MB)
2,774 (MB)
2,977 (MB)
3,075 (MB)[/font]
Those are all MSDN downloads though. The retail or RTM versions may differ slightly. Not sure.