NOTE: LedgerSMB has a Fixed assets module as of 1.3. The FAQ below is out-dated.
LedgerSMB does not have a built-in assett tracking / depreciation feature. Depreciation can be managed manually using General Ledger Transactions. You should probably confirm this with your accountant, but the basic procedure (kindly suggested by Tony Fraser) is, assuming a computer asset over 5 years: