--I would add parameters to minimize volume of information sent to client as well as internal processing overhaul (see below)
declare @filter sysname -- will be used to limit total number of records fetched and processes for SQL statement
    , @wait_time int -- we dont want alarm on healthy short-term blocking
    , @limit_sql_detection int -- will be used to limit number of SQL statements fetched per blocking chain branch 
    , @ignore_selfblocking bit
select @filter = N'blocking' -- {blocking | waits | all}
    , @limit_sql_detection =  3  -- <=0-do not fetch SQL at all, >0-number of SQL to detect per blocking chain branch
    , @wait_time =  1000  -- im milliseconds
    , @ignore_selfblocking =  1  

SET NOCOUNT ON
SET XACT_ABORT ON
--go in favor of temporary table for backward compatibility
if object_id('tempdb..#processes') is not null drop table #processes
create table #processes( 
	[spid] [smallint] NULL, 
	[blocked] [smallint] NULL, 
	[name] [nvarchar] ( 128 ) NULL,
	[waittime] [int] NULL , --changed from bigint for backward compatibility
	[lastwaittype] [nchar] ( 32 ) NULL ,
	[waitresource] [nchar] ( 256 ) NULL ,
	[open_tran] [smallint] NULL ,
	[status] [nchar] ( 30 ) NULL ,
	[hostname] [nchar] ( 128 ) NULL ,
	[program_name] [nchar] ( 128 ) NULL ,
	[cmd] [nchar] ( 16 ) NULL ,
	[loginame] [nchar] ( 128 ) NULL ,
	[cpu] [int] NULL ,
	[physical_io] [int] NULL , --changed from bigint for backward compatibility
	[memusage] [int] NULL,
	[last_batch] [datetime] NULL,
	[sql] [nvarchar] ( 500 ) NULL
)

if @@version not like 'Microsoft SQL Server  7%' --upconverting to SS2005, application code should be able to compensate the difference between versions
    exec ('alter table #processes alter column [waittime] [bigint] NULL;
        alter table #processes alter column [physical_io] [bigint] NULL;')

insert into #processes with(tablock)
select spid, blocked, d.name, waittime, lastwaittype, waitresource, open_tran, p.status, 
		hostname, program_name, cmd, loginame, cpu, physical_io, memusage, last_batch, ''
from master.dbo.sysprocesses p left outer join master..sysdatabases d on d.dbid = p.dbid

--filtering added
....