Here is the ARCserve 11.1 compatibility matrix.
Backup Agent for Microsoft SQL Server Windows NT 4.0 Server SP6a - SQL 7.0 Standard & Enterprise SP3
Windows 2000 Server SP4, SP4 Rollup 1 - SQL 7.0 Standard & Enterprise SP3
Windows 2000 Server SP4, SP4 Rollup 1 - SQL 2000 Standard SP3 & Enterprise SP2, SP3
Windows 2000 Adv.Server SP4, SP4 Rollup 1 - SQL 7.0 Enterprise SP3
Windows 2000 Adv.Server SP4, SP4 Rollup 1 - SQL 2000 Standard & Enterprise SP2, SP3
Windows 2000 Small Business Server - SQL 2000 Standard & Enterprise SP2, SP3
Windows 2003 Enterprise SP1 - SQL 2000 Standard & Enterprise SP2, SP3
Windows 2003 Small Business Server SP1 - SQL 2000 Standard & Enterprise SP2, SP3
Windows 2000, 2003 Microsoft SQL Server 2000 Desktop Engine (MSDE 2000)
However the 11.5 matrix does list SQL 2005
Windows 2003 Standard SP1 (32 bit) - SQL 2005 SP1(32 bit), SQL 2005 SP2 (32 bit)1
Windows 2003 Enterprise (IA-64, x64) SP1, SP2 - SQL 2005 (IA-64, x64), SQL 2005 SP1, SP2 (IA-64, x64)-- including Cluster1
Windows 2003 Standard R2, SP2 (32 bit, x64)1 - SQL 2005 (32 bit, x64), SP1, SP2
Windows 2003 Enterprise R2, SP2(32 bit, x64)1 - SQL 2005 (32 bit, x64), SQL 2005 SP1, SP2 (32 bit, x64) -- including Cluster
Windows Storage Server 2003 R2, SP2 (32 bit)1 -- SQL 2000 SP4, SQL 2005 SP1, SP2 (32 bit)
Windows Storage Server 2003 R2 (x64)1 -- SQL 2000 SP4 (32 bit), SQL 2005 SP1, SP2 (32 bit, x64)
SQL 2005 Supported Editions - Workgroup, Express, Enterprise, Standard, Developer Edition