Help............ SQL Query is too slow

Hi

I have a massive, inefficient query in SQL server 2000 database . This query is killing the processor and slows down the entire machine thus other computers are unable to get data from the SQL server. I have just taken over from the previous programmer who has written this query and I don't know much about SQL server. Please help and let me know how to optimize the query.

The query is as follows (I have copied it from the SQL Profiler):

exec sp_executesql N'select t1.jobid as [Lio No],case when len(t3.Name) > 15 then substring(t3.Name,0,15)+''...'' else t3.Name end AS [Client Name],t4.Name As [Matter/Ref],case when len(t1.Description) > 25 then substring(t1.Description,0,20)+'' ...'' else t1.Description end as [Job Description],SUBSTRING(t6.firstname,0,2)+ SUBSTRING(t6.lastName,0,2) as [Owner],convert(varchar, t1.TimeCreated,103)+ SubString(convert(varchar,  t1.TimeCreated,100),12,10) as [TimeIn],convert(varchar, t1.TimeDue,103)+ SubString(convert(varchar, t1.TimeDue,100),12,10) as [TimeDue],convert(varchar, dbo.[GetTimeSent](t1.JobId), 103) + SubString(convert(varchar, dbo.[GetTimeSent](t1.JobId),100),12,10) as [TimeSent],t7.JobStatusName as [Job Status],t1.TimeDue as [Time2],dbo.[GetTimeSent](t1.JobId) as [Time3],t6.firstname+ '' '' + t6.lastName as [FullOwnerName] ,t3.Name as  [ClientFullName],t2.FirstName + '' ''+ t2.LastName as [ContactName],case when len(t4.Name) > 25 then substring(t4.Name,0,20)+''...'' else t4.Name end as Matter,t1.Description as [FullDescription]  from lioe_jobs t1,lioe_contacts t2,lioe_clients t3,lioe_matters t4,lioe_jobTypes t5,USERS t6,lioe_jobs_Status t7 where  t1.MatterId=t4.MatterId and t1.JobTypeId = t5.JobTypeID and t1.OwnerId = t6.UserID and t1.Clientid=t3.clientid and t1.JobStatusId=t7.JobStatusId and t1.ContactId=t2.ContactId and  DateDiff(Month,t1.TimeDue,getDate()) like @MonthDue and DateDiff(day,t1.TimeDue,getDate()) like @DayDue and DateDiff(day,IsNull(t1.TimeCreated,01/01/2000),getDate()) like @DayIn and DateDiff(day,IsNull(dbo.[GetTimeSent](t1.JobId),01/01/2000),getDate()) like @DaySent and t1.JobId like @City and DateDiff(day,IsNull(t1.TimeCreated,getDate()),getDate()) between @TimeIn1 and @TimeIn2 and DateDiff(day,t1.TimeDue,getDate()) between @TimeDue1 and @TimeDue2 and DateDiff(day,IsNull(dbo.[GetTimeSent](t1.JobId),getDate()),getDate()) between @TimeSent1 and @TimeSent2 and DateDiff(Month,IsNull(t1.TimeCreated,getDate()),getDate()) like @TimeIn3 and DateDiff(Month,t1.TimeDue,getDate()) like @TimeDue3 and DateDiff(Month,IsNull(dbo.[GetTimeSent](t1.JobId),getDate()),getDate()) like @TimeSent3 Order By t1.TimeDue desc', N'@MonthDue nvarchar(1),@DayDue nvarchar(1),@DayIn nvarchar(1),@DaySent nvarchar(1),@City nvarchar(15),@TimeIn1 nvarchar(4),@TimeIn2 nvarchar(3),@TimeIn3 nvarchar(1),@TimeDue1 nvarchar(4),@TimeDue2 nvarchar(3),@TimeDue3 nvarchar(1),@TimeSent1 nvarchar(4),@TimeSent2 nvarchar(3),@TimeSent3 nvarchar(1),@Today nvarchar(1)', @MonthDue = N'%', @DayDue = N'%', @DayIn = N'0', @DaySent = N'%', @City = N'[A,C,D,E,][B,]%', @TimeIn1 = N'-365', @TimeIn2 = N'365', @TimeIn3 = N'%', @TimeDue1 = N'-365', @TimeDue2 = N'365', @TimeDue3 = N'%', @TimeSent1 = N'-365', @TimeSent2 = N'365', @TimeSent3 = N'%', @Today = N'%'


HELLLPPPPPP.............

Thanks a lot

AB