This code might help you out. Just take the deadlock XML info you posted above, put it into the @deadlock variable, and run.
declare @deadlock xml
set @deadlock = 'put your deadlock graph here'
select
[PagelockObject] = @deadlock.value('/deadlock-list[1]/deadlock[1]/resource-list[1]/pagelock[1]/@objectname', 'varchar(200)'),
[DeadlockObject] = @deadlock.value('/deadlock-list[1]/deadlock[1]/resource-list[1]/objectlock[1]/@objectname', 'varchar(200)'),
[Victim] = case when Deadlock.Process.value('@id', 'varchar(50)') = @deadlock.value('/deadlock-list[1]/deadlock[1]/@victim', 'varchar(50)') then 1 else 0 end,
[Procedure] = Deadlock.Process.value('executionStack[1]/frame[1]/@procname[1]', 'varchar(200)'),
[LockMode] = Deadlock.Process.value('@lockMode', 'char(1)'),
[Code] = Deadlock.Process.value('executionStack[1]/frame[1]', 'varchar(1000)'),
[ClientApp] = Deadlock.Process.value('@clientapp', 'varchar(100)'),
[HostName] = Deadlock.Process.value('@hostname', 'varchar(20)'),
[LoginName] = Deadlock.Process.value('@loginname', 'varchar(20)'),
[TransactionTime] = Deadlock.Process.value('@lasttranstarted', 'datetime'),
[InputBuffer] = Deadlock.Process.value('inputbuf[1]', 'varchar(1000)')
from @deadlock.nodes('/deadlock-list/deadlock/process-list/process') as Deadlock(Process)
From this, I see that you are running an UPDATE and a DELETE at the same time from your sharepoint portal (different procs).
If you were to look at the execution plans for these commands, I bet you would find that one or both is doing table scans, effectively locking the entire table.
Wayne
Microsoft Certified Master: SQL Server 2008
Author - SQL Server T-SQL Recipes