I don't have plans to retrofit it but just curious since this is a NA car.
Here are its options. Which one is it?

Data for vehicle identification number: 5UXFA93576LE84292
Model description: X5 4.8is
Market: USA
Type: FA93
E-Code: E53
Chassis: Sports Activity Vehicle
Steering: links
Doors: 5
Engine: N62B48O0 - 4,80l (265kW)
Drive: Allrad
Transmission: automatisch
Body Color: Le-mans-blau Metallic (381)
Upholstery: Exclusivleder Walknappa/schwarz (V9SW)
Production date: 10.02.2006
Assembled in: Spartanburg

S216A Servolenkung-Servotronic HYDRO STEERING-SERVOTRONIC
S221A 2-Achs-Niveauregulierung 2-axle self-levelling suspension
S226A Sportliche Fahrwerksabstimmung Sports suspension settings
S249A Multifunktion für Lenkrad Multifunction f steering wheel
S255A Sport-Lederlenkrad Airbag Sports leather steering wheel
S2KDA BMW LM Rad V-Speiche 168
S302A Alarmanlage Alarm system
S321A Exterieurumfänge in Wagenfarbe Exterior parts in vehicle color
S354A Frontscheibe grün Grünkeil Green windscreen, green shade band
S442A Getränkehalter Cup holder
S459A Sitzverstellung elektrisch mit Memory Seat adjuster, electric, with memory
S473A Armlehne vorne Armrest front
S481A Sportsitz Sports seat
S488A Lordosenstütze Fahrer u. Beifahrer Lumbar support, driver and passenger
S494A Sitzheizung Fahrer/Beifahrer Seat heating driver/passenger
S502A Scheinwerferreinigungsanlage Headlight cleaning system
S522A Xenon-Licht Xenon Light
S533A Fond-Klimatisierung Air conditioning, rear
S534A Klimaautomatik Automatic air conditioning
S645A BMW US Radio BMW US Radio
S775A Dachhimmel anthrazit Headlining anthracite
S785A Blinkleuchten weiss White direction indicator lights
S840A Hochgeschwindigkeitsabstimmung High speed synchronisation
S845A Akustische Gurtwarnung Acoustic belt warning
S853A Sprachversion englisch Language version English
S876A Funkfrequenz 315 MHz Radio frequency 315 MHz
S992A Steuerung Kennzeichenbefestigung Control of number-plate attachment
S1CAA Selektion COP relevanter Fahrzeuge Selection of COP relevant vehicles
S205A Automatikgetriebe Automatic transmission
S248A Lenkradheizung Steering wheel heater
S386A Dachreling Roof railing
S402A Panoramadach elektrisch Electric panoramic roof
S417A Sonnenschutzrollo Tür hinten Roller sun vizor, rear door
S430A Innen-/Aussensp. mit Abblendautomatik Interior/outside mirror with auto dip
S438A Edelholzausführung Fine wood trim
S441A Raucherpaket Smoker package
S464A Skisack Ski bag
S496A Sitzheizung hinten Seat heating, rear
S4NAA Innenspiegel mit digitalem Kompass Interior mirror with digital compass
S508A Park Distance Control (PDC) Park Distance Control (PDC)
S521A Regensensor Rain sensor
S524A Adaptives Kurvenlicht Adaptive Headlights
S548A Kilometertacho Kilometer-calibrated speedometer
S609A Navigationssystem Professional Navigation system Professional
S639A Vorbereitung Handy komplett USA/CDN Preparation f mobile phone cpl. USA/CDN
S672A CD-Wechsler 6-fach CD changer for 6 CDs
S677A HiFi System Professional DSP HiFi System Professional DSP
S691A CD-Halterung CD holder
S761A Individual Sonnenschutzverglasung Individual sunshade glazing
S818A Batteriehauptschalter Battery master switch
L838A Länderausführung Kanada NATIONAL VERSION CANADA
S896A Tagfahrlichtschaltung Daytime driving light switch
S8SPA Steuerung COP Control unit COP

Are you asking if the ACC option is listed? It's not...the option code for adaptive cruise control is S541A. There's obviously an issue with the cluster since the light is illuminated...and lots of BMWs have that same icon regardless if the option was offered in that BMW market. Most high instrument clusters have that icon.

Again, if the vehicle actually had ACC (adaptive cruise control)...not only would the icon be illuminated that you have circled in the pic below...but the green icon (for ACC would also be illuminated...as well as the little car icons in the Check Control display...which you set to determine the distance you want to follow:

Thanks Qsilver. It makes sense. Most likely it was just on the cluster and never hooked up for ACC.

No problem...and if you've never seen how ACC works on our generation BMWs...here's a link to a Euro E38 with ACC...the video is by Edwin (from the Netherlands...and friend to many e38 owners here in the States).

The video shows how the icons work and how you use the MFL buttons to set things up etc: http://youtu.be/vO5AdLOXeWs

why would this light keep coming on?

PO changed the "check engine light" bulb in the empty ACC socket :bustingup

LOL...

Figure I'll change the battery since wonky things has been going on with my X.