XML字符串，如何读取其中的元素值??高分。。不够再加

var
 STR:STRING;
str:='<?xml version="1.0" encoding="utf-8"?>
<SOAP-ENV:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
    xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/">
<SOAP-ENV:Header>
    <TransactionID xmlns="http://www.monternet.com/dsmp/schemas/">00230301659556</TransactionID>
</SOAP-ENV:Header>
<SOAP-ENV:Body>
<SyncOrderRelationReq xmlns="http://www.monternet.com/dsmp/schemas/"><Version>1.5.0</Version>
<MsgType>SyncOrderRelationReq</MsgType>
<Send_Address>
<DeviceType>0</DeviceType>
<DeviceID>0023</DeviceID>
</Send_Address>
<Dest_Address>
<DeviceType>400</DeviceType>
<DeviceID>0</DeviceID>
</Dest_Address>
<FeeUser_ID>
<UserIDType>1</UserIDType>
<MSISDN>13805002425</MSISDN>
<PseudoCode></PseudoCode>
</FeeUser_ID>
<DestUser_ID>
<UserIDType>1</UserIDType>
<MSISDN>13805002425</MSISDN>
<PseudoCode></PseudoCode>
</DestUser_ID>
<LinkID>SP</LinkID>
<ActionID>2</ActionID>
<ActionReasonID>1</ActionReasonID>
<SPID>911005</SPID>
<SPServiceID>-TDXY</SPServiceID>
<AccessMode>3</AccessMode>
<FeatureStr>YWJjZGVm</FeatureStr>
</SyncOrderRelationReq>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>'
比如我想读取</TransactionID>的值，delphi6做