if I understnad you correctly try and imbed your second query as sub queries in your first query. You only wan starting sums values for each partnumber...
Select P.PartNum, P.PartDescription,
PC.ClassID, PC.Description as 'Class Description',
PP.MinimumQty, PP.MaximumQty, PP.LeadTime, PP.MinOrderQty,
C.CustID, C.Name as 'Customer Name',
PB.WarehouseCode, PB.BinNum, PB.OnHandQty, PB.LotNum, V1.StartQty, V2.StartPurchase
From Part P
Inner Join PartClass PC on P.Company = PC.Company
and P.ClassID = PC.ClassID
Inner Join PartPlant PP on P.Company = PP.Company
and P.PartNum = PP.PartNum
Inner Join Customer C on P.Company = C.Company
and Left(P.ClassID,3) = C.CustID
Left Outer Join PartBin PB on P.Company = P.Company
and P.PartNum = PB.PartNum
left outer join
(Select PartNum, sum(TranQty) as StartQty
From PartTran PT1
Where TranType in ('Stk-Mtl', 'Stk-Cus')
and TranDate > DATEADD(YEAR,-1,GETDATE())
group by partnum) V1 on V1.partnum = P.partnum
left outer join
(Select PartNum, sum(TranQty) as StartPurchase
From PartTran PT2
Where TranType in ('Pur-Ins', 'Pur-Stk', 'Pur-Mtl', 'Pur-Ukn')
and TranDate > DATEADD(YEAR,-1,GETDATE())
group By PartNum) as V2 on V2.partnum = P.partnum
Where P.TypeCode = 'P'
Order By P.PartNum