Having worked as an Addictions Counsellor prior to Nursing I was faced with working with many patients with personality disorders, mostly antisocial, histrionic and borderline, but I also worked with patients who had a narcisistic, paranoid, depressive or dependent personality (not necessarily with the personality disorder as such, but at least with those characteristics in their personality). Approximately 1/3 of D&A cls/pts have an underlying PD.
One important consideration is not to label. It does not matter if they have had this Dx made recently or a long time ago, there may be other cause for the behaviour and it may be a temporary manifestation of a nervous breakdown, for instance. Also, many "normal" pts on a med/surg unit behave in a demanding manner and are not treated as a person with a personality disorder nor are they considered to have one. Often the functional or non-PD-related behaviour of the person with a PD is then interpreted as part of their disorder. This labelling can be a barrier to proper therapy much in the same way that known narcotic dependent people are often refused adequate pain relief.
A second consideration is that you may not be the only nurse working with this cl/pt. The attitudes of others will affect therapy. Of course, these cls/pts are known to be manipulative but remember that this should not affect the treatment goals, only the strategies used to achieve them. You might find it useful to have a discussion about BPD with your colleagues. A good way to go about it is to suggest a team meeting with a psychologist, social worker, psychiatrist and nurses. Then there is room for everybody to learn from each other's expertise and experiences in a positive environment, and it won't be coming from just one person.
I strongly recommend Marsha M. Linehan's (1993) book, Cognitive Behavioural Treatment of Borderline Personality Disorder (558 page hardback from Guilford press, which goes into the development of the disorder and the theories behind it. Linehan is the pioneer of Dialectic Behavioural Therapy and explains it very well in her book. I am sorry, but it is a complex therapy and I cannot offer any kind of summary here.
If you don't have time to read a whole book on the topic, I would at least recommend that you read the theory in Linehan's book so that you have a grounding in understanding the behaviour and what techniques will likely bring a good response. For instance, in a broad sense, the fact that many of the behaviours of BPD cls/pts stem from a lack of validation in their lives would help you to understand the importance of temporarily accepting some of the behaviours from these patients that you wouldn't accept from other cls/pts, and devising statements that confront the need for this behaviour while still validating the person's feelings/needs.
You also indicated that you had some difficulty working with more than one personality disordered cl/pt at a time. The best suggestion I can give you at this time is to treat each person individually unless you are doing groupwork, and to explain this to the cls/pts. That way you won't find yourself a victim of two or more ganging up on you.
I am also not sure of your facility's way of delegating pt assignments, but all units/facilities should have a policy on assessing (in a sense, triaging) the degree of load each pt demands. Pts/cls with a PD often pose a HEAVY load, so the rest of your assignment should consist of lighter pts. However, with a good deal of experience in dealing with these pts, you may find it increasingly easier to take on more of these kinds of pts.