How do I rewrite this to avoid a cursor - sql

Question

I have this function written in T-SQL on SQL Server 2005. I am not as against cursors as some are but I always see people saying 99% of all cursors can be re-written to avoid their use.
I have this function:
CREATE FUNCTION WhereUsed(#ItemID varchar(100))
RETURNS varchar(MAX)
AS
BEGIN
DECLARE #Items CURSOR
DECLARE #ParentItem varchar(100)
DECLARE #WhereUsed varchar(MAX)
SET #WhereUsed = ''
SET #Items = CURSOR FAST_FORWARD
FOR
SELECT PST_ParentItemID FROM PST WHERE PST_CompItemID = #ItemID
OPEN #Items
FETCH NEXT FROM #Items
INTO #ParentItem
WHILE ##FETCH_STATUS = 0
BEGIN
SET #WhereUsed = #WhereUsed + #ParentItem + ', '
FETCH NEXT FROM #Items
INTO #ParentItem
END
IF LEN(#WhereUsed) > 2
SET #WhereUsed = LEFT(#WhereUsed, LEN(#WhereUsed) - 2)
RETURN #WhereUsed
END
Which will get all the items where a part is used, PST is ParentStructureTable. Think BOM (Bill Of Materials)
It will be used like this:
SELECT Field1, Field2, dbo.WhereUsed(ItemID), Field3 FROM Item
And return something like this:
S6110-23350-41, 61070-10161-012, R6112-23027-41
How could this be done without using a cursor?
EDIT:
Sample data
SELECT PST_ParentItemID FROM PST WHERE PST_CompItemID = #ItemID
Can return
PST_ParentItemID
----------------
S6110-23350-41
61070-10161-012
R6112-23027-41
Its really a simple select statement, not sure how the DDL will help but here it is:
CREATE TABLE [dbo].[ProductStructure](
[PST_RecordID] [uniqueidentifier] NOT NULL,
[PST_PSH_RecordID] [uniqueidentifier] NOT NULL,
[PST_IMA_RecordID] [uniqueidentifier] NOT NULL,
[PST_EffStartDate] [datetime] NOT NULL,
[PST_EffStopDate] [datetime] NULL,
[PST_DisplayOrder] [int] NOT NULL CONSTRAINT [DF__ProdStruc__PST_DisplayOrder] DEFAULT ((0)),
[PST_Available] [bit] NOT NULL CONSTRAINT [DF__ProdStruc__PST_Available] DEFAULT ((1)),
[PST_AddDate] [datetime] NOT NULL CONSTRAINT [DF__ProdStruc__PST_AddDate__192BAC54] DEFAULT (getdate()),
[PST_QtyPerAssy] [float] NOT NULL CONSTRAINT [DF__ProdStruc__PST_QtyPerA__1A1FD08D] DEFAULT ((1)),
[PST_ScrapQty] [float] NOT NULL CONSTRAINT [DF__ProdStruc__PST_ScrapQt__1B13F4C6] DEFAULT ((0)),
[PST_PlanType] [nvarchar](11) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL CONSTRAINT [DF__ProdStruc__PST_PlanTyp__1C0818FF] DEFAULT ('MRP'),
[PST_ScrapPercent] [float] NOT NULL CONSTRAINT [DF__ProdStruc__PST_ScrapPe__1CFC3D38] DEFAULT ((0)),
[PST_LeadTimeOffsetDays] [smallint] NOT NULL CONSTRAINT [DF__ProdStruc__PST_LeadTim__1DF06171] DEFAULT ((0)),
[PST_RoutSeqID] [nvarchar](10) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
[PST_EngChangeOrderID] [nvarchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
[PST_FindID] [nvarchar](5) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
[PST_Comments] [ntext] COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
[PST_UseAbsQtyFlag] [bit] NOT NULL CONSTRAINT [DF__ProdStruc__PST_UseAbsQ__1EE485AA] DEFAULT ((0)),
[PST_IgnoreCostFlag] [bit] NOT NULL CONSTRAINT [DF__ProdStruc__PST_IgnoreC__1FD8A9E3] DEFAULT ((0)),
[PST_PlanningPercent] [float] NOT NULL CONSTRAINT [DF__ProdStruc__PST_Plannin__20CCCE1C] DEFAULT ((0)),
[PST_EMP_RecordID] [uniqueidentifier] NULL,
[PST_LastModifiedDate] [datetime] NULL,
[PST_PurchPOWO] [bit] NOT NULL CONSTRAINT [DF__ProdStruc__PST_PurchPO__21C0F255] DEFAULT ((0)),
[PST_AgileCreatedDate] [datetime] NULL,
[PST_ArchiveDate] [datetime] NULL,
[PST_UserDef1] [nvarchar](255) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
[PST_UserDef2] [nvarchar](255) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
[PST_UserDef3] [nvarchar](255) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
[PST_UserDef4] [nvarchar](255) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
[PST_UserDef5] [nvarchar](255) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
[timestamp] [timestamp] NULL,
[PST_SWImportFlag] [bit] NOT NULL CONSTRAINT [DF_ProductStructure_PST_SWImportFlag] DEFAULT ((0)),
[PST_CopiedFromRecordID] [uniqueidentifier] NULL,
[PST_OnPicklist] [bit] NOT NULL DEFAULT ((1)),
[PST_CID_DocumentID] [nvarchar](50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
CONSTRAINT [PK_ProductStructure] PRIMARY KEY NONCLUSTERED
(
[PST_RecordID] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

Answer 1

It appears you are simply returning a concatenated string. Try this
DECLARE #WhereUsed varchar(MAX)
SET #WhereUsed = ''
SELECT #whereUsed=#whereUsed+PST_ParentItemID+', 'FROM PST
WHERE PST_CompItemID = #ItemID
IF LEN(#WhereUsed) > 2
SET #WhereUsed = LEFT(#WhereUsed, LEN(#WhereUsed) - 2)