[Mogul, XV6800 ROM Development] scrawnyb:
It's in HKCU\ControlPanel\Notifications (see below for a reg file)

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\ControlPanel\Notifications]

[HKEY_CURRENT_USER\ControlPanel\Notifications\Phone]
"Options"=dword:80000000
@="Phone: Incoming call"
"DisplayOrder"=dword:00000001
"Wave"="\\Windows\\Ring-WindowsMobile .wma"
"Duration"=dword:00000001

[HKEY_CURRENT_USER\ControlPanel\Notifications\{A877D658-239C-47a7-9304-0D347F580408}]
@="ActiveSync: Begin sync"
"Wave"="infbeg"
"Duration"=dword:00000000
"AvailableOptions"=dword:00000003
"Options"=dword:00000000

[HKEY_CURRENT_USER\ControlPanel\Notifications\{A877D659-239C-47a7-9304-0D347F580408}]
@="ActiveSync: End sync"
"Wave"="infend"
"Duration"=dword:00000000
"AvailableOptions"=dword:00000003
"Options"=dword:00000000

[HKEY_CURRENT_USER\ControlPanel\Notifications\{F55615D6-D29E-4db8-8C75-98125D1A7253}]
@="Beam: Autoreceive"
"Wave"="\\Windows\\Loudest.wav"
"Duration"=dword:00000000
"Options"=dword:00000009

[HKEY_CURRENT_USER\ControlPanel\Notifications\{8ddf46e8-56ed-4750-9e58-afc6ce486d03}]
@="Connection disconnected"
"Wave"="infend"
"Duration"=dword:00000000
"AvailableOptions"=dword:00000003
"Options"=dword:00000000

[HKEY_CURRENT_USER\ControlPanel\Notifications\{8ddf46e7-56ed-4750-9e58-afc6ce486d03}]
"Options"=dword:00000000
@="Connection established"
"Wave"="infbeg"
"Duration"=dword:00000000
"AvailableOptions"=dword:0000000B

[HKEY_CURRENT_USER\ControlPanel\Notifications\{A877D65A-239C-47a7-9304-0D347F580408}]
"Wave"="\\Windows\\Alert-Sonar.wma"
"Options"=dword:0000000F
@="Messaging: New e-mail message"
"Duration"=dword:00000000

[HKEY_CURRENT_USER\ControlPanel\Notifications\{A877D65B-239C-47a7-9304-0D347F580408}]
"Wave"="\\Windows\\Alert-Soft.wma"
"Options"=dword:0000000F
@="Messaging: New text message"
"Duration"=dword:00000000

[HKEY_CURRENT_USER\ControlPanel\Notifications\{A877D660-239C-47a7-9304-0D347F580408}]
"Wave"="\\Windows\\Failure.wav"
"Options"=dword:0000000F
"Duration"=dword:00000000
@="Phone: Missed call"

[HKEY_CURRENT_USER\ControlPanel\Notifications\{A877D661-239C-47a7-9304-0D347F580408}]
"Wave"="\\Windows\\Buzz.wav"
"Options"=dword:0000000F
@="Phone: Voice mail"
"Duration"=dword:0000000F

[HKEY_CURRENT_USER\ControlPanel\Notifications\{15F11F90-8A5F-454c-89FC-BA9B7AAB0CAD}]
"Options"=dword:4000001F
"Duration"=dword:00000000
@="Reminders"
"Wave"="\\Windows\\notify.wma"

[HKEY_CURRENT_USER\ControlPanel\Notifications\{DDBD3B44-80B0-4b24-9DC4-839FEA6E559E}]
"Options"=dword:00000001
@="Wireless network detected"
"Wave"="\\Windows\\Default.wav"
"Duration"=dword:00000000

[HKEY_CURRENT_USER\ControlPanel\Notifications\ShellOverrides]
"Mode"=dword:00000000

[HKEY_CURRENT_USER\ControlPanel\Notifications\Default]
"LedRefCount"=hex:00,00,00,00
"Options"=dword:00000009
"Wave"="\\Windows\\Alarm2.wav"
"Duration"=dword:00000005

[HKEY_CURRENT_USER\ControlPanel\Notifications\{C3465585-39EF-4c9b-B2A3-5558BF27BFB0}]
"Options"=dword:00000003

[HKEY_CURRENT_USER\ControlPanel\Notifications\{3C781384-05F3-4035-A8F9-C23F19A93AF0}]
"Options"=dword:00000001

[HKEY_CURRENT_USER\ControlPanel\Notifications\{A877D65D-239C-47a7-9304-0D347F580408}]
"Wave"="online.wma"
"Duration"=dword:00000003
"Options"=dword:0000000D

[HKEY_CURRENT_USER\ControlPanel\Notifications\{B67B425B-365E-42c0-95F7-B75503D775B8}]
"Duration"=dword:00000000
"Options"=dword:00000008

[HKEY_CURRENT_USER\ControlPanel\Notifications\{0D3132C4-1298-469c-B2B8-F28CE2D649D0}]
"Wave"="infbeg"
"Duration"=dword:00000000
"Options"=dword:00000009

[HKEY_CURRENT_USER\ControlPanel\Notifications\{A877D663-239C-47a7-9304-0D347F580408}]
"Wave"="lowbatt.wma"
"Duration"=dword:00000000
"Options"=dword:00000009

[HKEY_CURRENT_USER\ControlPanel\Notifications\{E0F2B9DD-EDC6-45d4-B440-2C5B5A04A3E3}]
"Options"=dword:00000008

[HKEY_CURRENT_USER\ControlPanel\Notifications\Sounds]
"Repeat"=dword:00000000

[HKEY_CURRENT_USER\ControlPanel\Notifications\Reminders]

[HKEY_CURRENT_USER\ControlPanel\Notifications\Reminders\AutoSnooze]
"AutoSnoozeMins"=dword:00000002

Hope this helps.