David,
Checking Malcolm Webster’s posting history he hasn’t posted on the boards since March 2011; I hope all is well with him.
This should help you progress further.
From the Nominal Roll images for the Imperial Light Infantry first page of surname S at:
http://angloboerwar.com/unit-information/south-african-units > Imperial Light Infantry
Smith Donald Geo, Capt., 23.11.99, Removed from service 22.8.00
Enrolment Forms of the I.L.I. for the Smith surname are preserved at the National Archives Kew in:
WO 126/63 War Office: Local Armed Forces, Enrolment Forms, South African War; Imperial Light Horse and Imperial Light Infantry. Ro-So; 1899-1902
You can request an estimate for the NA staff to extract his form and copy it or you could request a private researcher for the same; relative costs are £25 GBP per 15 min for NA vs £30 - £40 GBP per hour for a researcher – see
http://www.nationalarchives.gov.uk/records/paid_research.htm