Common "Open File" dialog may contain "Places Bar" (left side bar) from which you can switch directly to frequently visited folders.

It's possible to change items in "Places Bar" accordingly to your needs. To do so you may run Regedit program and make changes manually, or you may run reg-file and all changes will be done at time it loads information into Windows Registry. In last case - open a new file in Notepad (or any other text editor), copy and paste information below into this new file, make your customization in "PlaceX" (where X is in range 0 - 4) values accordingly to your needs. Then save file, open CMD dialog, and run it from there. Changes will be effective immediately - no reboot is required.

Note - Office Products do not use common "File Open" dialog. They have its own dialog box that is customizable by its "Tools" menu.

Content of "OpenFile_PlaceBar.reg" file is below:
----------------
REGEDIT4

; Organizes Places Bar (left side bar) in common "File Open" dialogs.
;
; It's possible to use these 'dword' values to address standard folders:
; 00 - Desktop
; 01 - Internet Explorer
; 02 - Start Menu\Programs
; 03 - My Computer\Control Panel
; 04 - My Computer\Printers
; 05 - My Documents
; 06 - Favorites
; 07 - Start Menu\Programs\Startup
; 08 - \Recent
; 09 - \SendTo
; 0a - \Recycle Bin
; 0b - \Start Menu
; 0c - - logical "My Documents" desktop icon
; 0d - My Music
; 0e - My Videos
; 0f - -
; 10 - \Desktop
; 11 - My Computer
; 12 - My Network Places
; 13 - \NetHood
; 14 - WINDOWS\Fonts
; 15 - Templates
; 16 - All Users\Start Menu
; 17 - All Users\Programs
; 18 - All Users\Start Menu
; 19 - All Users\Desktop
; 1a - \Application Data
; 1b - \PrintHood
; 1c - \Local Settings\Application Data
; 1d - - Nonlocalized startup
; 1e - - Nonlocalized common startup
; 1f - Favorites
; 20 - Temporary Internet Files
; 21 - Cookies
; 22 - History
; 23 - All Users\Application Data
; 24 - WINDOWS directory
; 25 - System32 directory
; 26 - Program files
; 27 - My Pictures
; 28 - USERPROFILE
; 29 - - x86 system directory on RISC
; 2a - - x86 C:\Program Files on RISC
; 2b - C:\Program Files\Common
; 2c - - x86 Program Files\Common on RISC
; 2d - All Users\Templates
; 2e - All Users\Documents
; 2f - All Users\Start Menu\Programs\Administrative Tools
; 30 - - \Start Menu\Programs\Administrative Tools
; 31 - Network and Dial-up Connections
; 35 - All Users\My Music
; 36 - All Users\My Pictures
; 37 - All Users\My Video
; 38 - Resource Directory
; 39 - Localized Resource Directory
; 3a - Links to All Users OEM specific apps
; 3b - USERPROFILE\Local Settings\Application Data\Microsoft\CD Burning
; or use string values with specifying path to the folder (don't forget to
; put double '\\' in places, where '\' required as path delimiter).
;
; Default: key "Placesbar" is absent
;
; OZO, 2003

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\comdlg32\Placesbar]

"Place0"=dword:00000011 ; My Computer
"Place1"=dword:00000005 ; My Documents
"Place2"="C:\\Sys"
"Place3"="C:\\Temp"
"Place4"="C:\\WWW"
----------------
In this reg-file you see an example of places used in "Places Bar". Make changes of "PlacesX" values or remove unwanted values.

To restore original look of "Places Bar" - just remove "Placesbar" key from Registry or create "OpenFile_PlaceBar-.reg" from the content below and run it the same way as described above.
----------------
REGEDIT4

; Restores Place Bar (left side bar) in common "Open File" dialogs.
;
; Default: key "Placesbar" is absent
;
; OZO, 2003

[-HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\comdlg32\Placesbar]
----------------
Changes will take effect immediately.

If you need to hide "Places Bar" (I don't know why you'd do it) - put new value into the "comdlg32" key:
"NoPlacesBar"=dword:00000001
You have to restart running applications to see the change.

Be noticed - all modifications described above done on a per user basis.
OS required - Windows 2000, XP, 2003.